Research
Alternate Healthy Eating Index 2010 and risk of chronic obstructive pulmonary disease among US women and men: prospective study
BMJ 2015; 350 doi: http://dx.doi.org/10.1136/bmj.h286 (Published 03 February 2015) Cite this as: BMJ 2015;350:h286
- Raphaëlle Varraso, researcher12,
- Stephanie E Chiuve, assistant professor of medicine3, research associate4,
- Teresa T Fung, adjunct professor4, professor5,
- R Graham Barr, assistant professor of medicine and epidemiology6,
- Frank B Hu, professor478,
- Walter C Willett, professor478,
- Carlos A Camargo, professor789
- Correspondence to: R Varraso raphaelle.varraso@inserm.fr
- Accepted 10 December 2014
Abstract
Objective
To investigate the association between the Alternate Healthy Eating
Index 2010 (AHEI-2010)—a measure of diet quality—and the risk of chronic
obstructive pulmonary disease (COPD).
Design Prospective cohort study.
Setting Participants in the Nurses’ Health Study and the Health Professionals Follow-up Study, United States.
Participants 73 228 female nurses from 1984 to 2000 and 47 026 men from 1986 to 1998, who completed biennial questionnaires.
Main outcome measures
The primary outcome was the self report of newly diagnosed COPD.
Multivariable Cox proportional hazards models were adjusted for age,
physical activity, body mass index, total energy intake, smoking, second
hand tobacco exposure (only in the Nurses’ Health Study),
race/ethnicity, physician visits, US region, spouse’s highest
educational attainment (only in the Nurses’ Health Study), and
menopausal status (only in the Nurses’ Health Study).
Results
Over the study period, 723 cases of newly diagnosed COPD occurred in
women and 167 in men. In the pooled analysis, a significant negative
association was seen between the risk of newly diagnosed COPD and fifths
of the AHEI-2010: hazard ratios were 0.81 (95% confidence interval 0.51
to 1.29) for the second fifth, 0.98 (0.80 to 1.18) for the third fifth,
0.74 (0.59 to 0.92) for the fourth fifth, and 0.67 (0.53 to 0.85) for
participants who ate the healthiest diet according to the AHEI-2010
(that is, were in the highest fifth), compared with those who ate the
less healthy diet (participants in the lowest fifth). Similar findings
were observed among ex-smokers and current smokers.
Conclusions
A higher AHEI-2010 diet score (reflecting high intakes of whole grains,
polyunsaturated fatty acids, nuts, and long chain omega-3 fats and low
intakes of red/processed meats, refined grains, and sugar sweetened
drinks) was associated with a lower risk of COPD in both women and men.
These findings support the importance of a healthy diet in
multi-interventional programs to prevent COPD.
Introduction
Chronic
respiratory diseases remain a worldwide public health problem.
Respiratory health and lung function strongly predict general health
status and all cause mortality.1
In the 2010 Global Burden of Disease report, chronic obstructive
pulmonary disease (COPD) was the third most common cause of death
worldwide.2
The predominant risk factor for COPD in the developed world is
cigarette smoking, but up to one third of COPD patients have never
smoked, suggesting that other factors are involved. Apart from smoking,
relatively little attention has been paid to other modifiable risk
factors that might decrease the risk of developing COPD. Diet is one of
such factor, but prospective data on the association between diet and
the risk of COPD remain scarce,3
compared with the extensive literature on cardiovascular diseases or
cancer. A potential positive association of a diet rich in antioxidants
with better lung function and reduced long term mortality due to COPD
has been reported, as well as a negative association with a Western
diet, and more precisely with cured meat intake.4 5 6 7 8
Several
diet quality indices, usually based on established nutrient
requirements and well publicized dietary guidelines, have been developed
to evaluate the healthfulness of individual diets. These scores,
reflecting overall diet quality, can help researchers to sort through
the nutrient and food specific findings and provide a measure of diet
that incorporates nutrient and food interactions of likely biological
importance.9 10 11
Moreover, the scores are easy for clinicians and dietitians to use for
recording people’s diet in the clinic setting. Recently, a new measure
of diet quality was proposed that is more accurate than previous scores
as it is based on current scientific knowledge: the Alternate Healthy
Eating Index 2010 (AHEI-2010).12
This diet score, including 11 components, was associated with a 16%
lower risk of major chronic diseases (cardiovascular disease, diabetes,
and cancer).12
Several studies have confirmed the relevance of the AHEI-2010 diet
score as being associated with lower risk of total prostate cancer,13 lower incidence of obesity,14 healthy ageing and wellbeing,15 lower risk of hip fracture,16 and a reduced risk of all cause, cardiovascular, and cancer mortality.17
In
the context of tackling chronic diseases, public health initiatives to
improve lung function through dietary advice are particularly relevant
and timely. We therefore investigated prospectively the association
between the AHEI-2010 and the risk of newly diagnosed COPD in two large
prospective US cohorts, the Nurses’ Health Study and the Health
Professionals Follow-up Study.18 19
Methods
Overview
The
Nurses’ Health Study began in 1976, when 121 701 female nurses aged
30-55 years and living in 11 US states responded to a mailed health
questionnaire.18
The Health Professionals Follow-up Study began in 1986 when 51 529 male
US health professionals aged 40-75 years answered a detailed mailed
questionnaire that included a diet survey and items on lifestyle
practice and medical history.19
In both the Nurses’ Health Study and the Health Professionals Follow-up
Study, follow-up questionnaires were sent every two years thereafter to
update information on smoking habits, physical activity, weight, and
other risk factors and to ask about newly diagnosed medical conditions.
Participants also completed a food frequency questionnaire in 1984 for
the Nurses’ Health Study and at baseline (1986) for the Health
Professionals Follow-up Study. Similar food frequency questionnaires
were sent every two to four years thereafter (see web appendix 1).
We used several exclusion criteria in our analysis. The first category was related to the analysis of dietary data,20
and the second category was related to the analysis of cohort data.
Regarding dietary data, we excluded participants without a completed
food frequency questionnaire at baseline and participants with
unreasonably high (>3500 kcal/day for women and >4200 kcal/day for
men) or low intakes (<500 kcal/day for women and <800 kcal/day
for men) to take care of outliers, as well as those who had left more
than 70 items blank.20
We also excluded women and men who reported a diagnosed asthma or COPD
at baseline. The final baseline population included 73 228 women and
47 026 men.
Assessment of dietary intake
Dietary
intake information was collected by a food frequency questionnaire
designed to assess average food intake over the previous 12 months.
Standard portion sizes were listed with each food. For each food item,
participants indicated their average frequency of consumption over the
previous year in terms of the specified serving size by checking one of
nine frequency categories ranging from “almost never” to “at least six
times/day.” The selected frequency category for each food item was
converted to a daily intake. For example, a response of “one
serving/week” was converted to 0.14 servings/day.
Scoring criteria for the Alternate Healthy Eating Index 2010 are described in detail elsewhere.12
Briefly, the AHEI-2010 is based on 11 components: six components for
which the highest intakes were supposed to be ideal (vegetables, fruit,
whole grains, nuts and legumes, long chain omega-3 fats (docosahexaenoic
acid and eicosapentaenoic acid), and polyunsaturated fatty acids ), one
component for which moderate intake was supposed to be ideal (alcohol),
and four components for which avoidance or lowest intake were supposed
to be ideal (sugar sweetened drinks and fruit juice, red and processed
meat, trans fat, and sodium). Each component is given a minimal score of
0 and a maximal score of 10, with intermediate values scored
proportionally, and has the potential to contribute 0-10 points to the
total score. All the component scores are summed to obtain a total
AHEI-2010 score, which ranges from 0 to 110, with a higher score
representing a healthier diet (see web appendix 2 for the distribution
of the baseline score in each cohort—that is, AHEI-2010 calculated in
1984 for the Nurses’ Health Study and in 1986 for the Health
Professionals Follow-up Study).
We identified the
AHEI-2010 score from each food frequency questionnaire administrated in
1984, 1986, 1990, 1994, and 1998 in the Nurses’ Health Study and in
1986, 1990, and 1994 in the Health Professionals Follow-up Study. To
reduce measurement errors and to represent long term dietary intake, we
calculated the cumulative average of AHEI-2010, divided it into fifths,
and used it as a time dependent variable. The cumulative average
incorporated repeated measures of diet. For example, by using this
method in the Health Professionals Follow-up Study, we used the 1986
AHEI-2010 to predict newly diagnosed COPD in 1986-90, an average of the
1986 and 1990 AHEI-2010 to predict COPD in 1990-94, and the average of
the 1986, 1990, and 1994 AHEI-2010, to predict COPD from 1994 to 1998.
Assessment of respiratory phenotypes
In
1998 and 2000 a supplemental questionnaire on COPD was sent to every
participant who reported a physician’s diagnosis of emphysema or chronic
bronchitis before 1996 (on the biennial questionnaire). The specific
questionnaire included, among other data, information confirming a
physician’s diagnosis of emphysema, chronic bronchitis, or COPD, as well
as the dates of symptom onset and diagnosis and the tests performed to
confirm the diagnosis or symptoms consistent with a diagnosis of chronic
bronchitis. Self reported COPD was defined by the affirmative response
to a physician’s diagnosis of chronic bronchitis or emphysema and by the
report of a diagnostic test at diagnosis (that is, pulmonary function
testing, chest radiograph, or chest computed tomography was performed).
This epidemiologic definition was validated in a random sample of COPD
cases in the Nurses’ Health Study.21
We obtained participants’ medical records, and a physician reviewed
them in a blinded fashion. The diagnosis of COPD was confirmed in 80% of
218 cases that met this case definition and 88% of cases that met this
definition and denied a physician’s diagnosis of asthma. Results of
pulmonary function testing were available in the medical records of 71%
of confirmed cases; the mean forced expiratory volume in one second (FEV1) in this group was 50% of predicted.
Asthma
was also self reported and was defined by a doctor’s diagnosis of
asthma and the use of drugs for asthma within the previous 12 months. We
validated the self reported incidence of asthma against medical records
for a random sample of 100 cases in a related study of female nurses
and confirmed that all carried a physician’s diagnosis of asthma.22
Assessment of others variables
When
possible, covariates were obtained from the baseline questionnaire
(1984 in Nurses’ Health Study, and 1986 in Health Professionals
Follow-up Study) and updated every two years. Variables included time
varying covariates such as age, physical activity, body mass index,
total energy intake, smoking status, pack years of smoking, and
menopausal status (only in the Nurses’ Health Study) and fixed
covariates such as second hand tobacco exposure (only in the Nurses’
Health Study), race/ethnicity, physician visits, US region, and spouse’s
highest educational attainment (only in the Nurses’ Health Study).
Physical
activity, including a variety of activities such as walking, cycling,
swimming, or playing tennis, was measured in metabolic equivalents per
week and used as a continuous variable. Body mass index (calculated as
kg/m2) was updated biennially and categorized in four
categories (<20.0, 20.0-24.9, 25.0-29.9, and ≥30.0). Total energy
intake was estimated through the food frequency questionnaire, expressed
in kilocalories per day, and used as a continuous variable. Smoking
status was categorized as never smoker, ex-smoker, or current smoker.
Pack years of smoking were calculated among ever-smokers. Second hand
tobacco exposure was defined by an exposure at home, work, or both.
Race/ethnicity was categorized in two groups (white, non-white).
Examination by a physician in the previous two years was categorized in
three classes (no visit, screening visit, symptoms related visit), and
US region was categorized in six classes (New England, Mid-Atlantic,
East North Central, South Atlantic, West South Central, Pacific). Among
women, spouse’s educational attainment was categorized in three classes
(high school, college, or graduate school), and menopausal status was
categorized in five categories as pre/postmenopausal and according to
whether estrogen or progesterone replacement (oral or patch) had been or
was being used (premenopause, postmenopause and never hormone
replacement therapy use, postmenopause and past user of replacement
therapy, postmenopause and estrogen replacement therapy, post-menopause
and estrogen-progesterone replacement therapy).
Bias
Residual
confounding by smoking remains an important source of possible bias in
studies of respiratory diseases and diet. In our particular study, in
which both smoking and COPD were self reported, we faced an unusually
high risk of residual confounding. As smoking is the major risk factor
for COPD, we further investigated the association among ex-smokers and
current smokers (the number of newly diagnosed COPD cases among never
smokers was too small to conduct a meaningful analysis). We also
excluded participants with previous comorbidities (cardiovascular
diseases and cancer). To avoid potential for preclinical COPD leading to
reverse causation, we did “lagged” analyses, by omitting the cases from
the initial four years of follow-up, and further examined the long
latency of COPD, by omitting the cases from the initial eight years of
follow-up.
Statistical analysis
We
analyzed the association between the risk of COPD and the cumulative
average of the AHEI-2010 score (that is, time varying exposure) by using
a stratified proportional Cox hazards model adjusted for time varying
variables (physical activity, body mass index, total energy intake,
smoking status, pack years of smoking, pack years2 of
smoking, and menopausal status (only in the Nurses’ Health Study)) and
fixed variables (second hand tobacco exposure (only in the Nurses’
Health Study), race/ethnicity, physician visits, US region, and spouse’s
highest educational attainment (only in the Nurses’ Health Study)). The
proportional hazards model was stratified according to age (in months)
to provide finer control for age. In addition, we analyzed each
individual component of the AHEI-2010 diet score by using Cox
proportional hazards model adjusted for the same potential confounders
plus the other AHEI-2010 components.
To minimize missing
continuous covariates (physical activity, total energy intake, and pack
years of smoking), we replaced missing data on these three covariates
with the last valid values. For missing data on these continuous
covariates at baseline, we created a dummy variable when making
categories for these continuous covariates. Similarly, we used missing
indicator variables to include participants with missing categorical
variables, including smoking status, second hand tobacco exposure
(Nurses’ Health Study only), body mass index, menopausal status (Nurses’
Health Study only), race/ethnicity, physician visits, US region, and
spouse’s highest educational attainment (Nurses’ Health Study only). In
the Nurses’ Health Study, the percentage of missing values at baseline
was 0.3% for smoking, 1.5% for second hand tobacco exposure, 4.9% for
body mass index, 10.2% for menopausal status, 0.8% for race/ethnicity,
11.2% for physician visits, 0% for US region, and 24.1% for spouse’s
educational attainment. In the Health Professionals Follow-up Study, the
percentage of missing values at baseline was 3.8% for smoking, 0% for
body mass index, 0.2% for race/ethnicity, 14.2% for physician visits,
and 0% for US region. In both cohorts, after adjustments for pack years
and pack years2 of smoking, the missing smoking status category was not associated with the risk of newly diagnosed COPD.
We
calculated a test for trend across the fifths of the AHEI-2010 score by
treating the categories as an ordinal variable in a proportional
hazards model. After calculating sex specific hazard ratios, we combined
the loge hazard ratios, weighted by the inverse of their variances, by using a random effects model.23
We tested for between studies heterogeneity by using the Q statistic,
which gives information about the presence versus the absence of
heterogeneity, and we also provided the I2 index to quantify the degree of heterogeneity between studies, expressed as a percentage of total variance.23 We calculated two sided 95% confidence intervals. We used SAS version 9.3 for all analyses.
Results
Characteristics of population
Tables 1⇓ and 2⇓
shows characteristics of women and men according to fifths of the
AHEI-2010. Among both women and men, those with the highest score for
AHEI-2010 (highest fifth, healthy diet) were more physically active,
less often obese, and less likely to be current smokers than those with
the lowest AHEI-2010 score (lowest fifth, unhealthy diet). Among women,
those with the highest scores for AHEI-2010 were less exposed to
secondhand smoke at work and at home than were those with the lowest
scores for AHEI-2010. In the Nurses’ Health Study, 45% of the women were
never smokers at baseline, 32% were former smokers, and 23% were
current smokers. Among former smokers, 62% had quit smoking at least 10
years before; only 10% had quit in the previous two years. In the Health
Professionals Follow-up Study, 47% of the men were never smokers at
baseline, 43% were former smokers, and only 10% were current smokers.
Among former smokers, 72% had quit smoking at least 10 years before;
only 8% had quit in the previous two years.
Table 1
Age standardized baseline characteristics in women (Nurses’ Health
Study; n=73 228) according to fifths of Alternate Healthy Eating Index
2010 (AHEI-2010). Values are percentages (standardized to age
distribution of study population) unless stated otherwise
Table 2
Age standardized baseline characteristics in men (Health Professionals
Follow-up Study; n=47 026) according to fifths of Alternate Healthy
Eating Index 2010 (AHEI-2010). Values are percentages (standardized to
age distribution of study population) unless stated otherwise
Alternate Healthy Eating Index 2010 and COPD
Among
women in the Nurses’ Health Study, we documented 723 cases of newly
diagnosed COPD between 1984 and 2000 (from 1 137 106 person years);
among men in the Health Professionals Follow-up Study, 167 cases were
reported between 1986 and 1998 (from 521 764 person years). The
incidence rate for newly diagnosed COPD was 64 per 100 000 person years
in the Nurses’ Health Study and 32 per 100 000 person years in the
Health Professionals Follow-up Study.
In the pooled
analysis, the risk of newly diagnosed COPD was inversely associated with
the AHEI-2010 diet score: the age adjusted hazard ratio for the highest
compared with the lowest fifth of AHEI-2010 score was 0.32 (95%
confidence interval 0.25 to 0.40; P for trend<0.001), with no
heterogeneity between studies (P=0.50). After control for several
potential confounders (table 3⇓),
the risk of newly diagnosed COPD was one third lower in participants
who ate the healthiest diet according to the AHEI-2010 (highest fifth)
compared with those who ate the least healthy diet (lowest fifth): the
multivariable hazard ratio was 0.67 (0.53 to 0.85). In both women and
men, the healthiest diet was associated with a reduced risk of newly
diagnosed COPD: multivariable hazard ratios for the highest compared
with the lowest fifth of AHEI-2010 score were 0.69 (0.53 to 0.90) in
women and 0.60 (0.34 to 1.03) in men, with no heterogeneity between
studies (P=0.63).
Table 3
Association between Alternate Healthy Eating Index 2010 (AHEI-2010) and
risk of newly diagnosed chronic obstructive pulmonary disease in women
(Nurses’ Health Study) and men (Health Professionals Follow-up Study)
We
also investigated the association between AHEI-2010 and the risk of
newly diagnosed COPD in ex-smokers and current smokers (table 4⇓).
In the pooled analysis, after control for several potential
confounders, the risk of newly diagnosed COPD was inversely associated
with the AHEI-2010 diet score both in ex-smokers (P for trend=0.002) and
in current smokers (P for trend=0.03). The hazard ratio for the highest
compared with the lowest fifth of AHEI-2010 score in ex-smokers was
0.50 (0.33 to 0.75), and in current smokers it was 0.69 (0.49 to 0.98).
The findings were similar in women and men. Among ever smokers, we
further investigated the interaction between the AHEI-2010 score and
pack years of smoking, but the association was not significant (P=0.42).
Table 4
Association between Alternate Healthy Eating Index 2010 (AHEI-2010) and
risk of newly diagnosed chronic obstructive pulmonary disease in women
(Nurses’ Health Study) and men (Health Professionals Follow-up Study),
according to smoking status
In
a sensitivity analysis looking at a study population without cancer or
cardiovascular disease at baseline (n=105 220 participants, with 771
cases of newly diagnosed COPD), we observed similar associations between
AHEI-2010 and the risk of newly diagnosed COPD. In the pooled analysis,
after adjustments for potential confounders, the healthiest diet was
associated with a reduced risk of newly diagnosed COPD: the
multivariable hazard ratio for the highest compared with the lowest
fifth of AHEI-2010 score was 0.71 (0.55 to 0.92) (P for trend=0.007; P
for between studies heterogeneity=0.62).
We also did
lagged analyses, firstly by excluding cases occurring in the first four
years (n=207). We again observed a strong negative association between
the AHEI-2010 and the risk of newly diagnosed COPD: the pooled
multivariable hazard ratio for the highest compared with the lowest
fifth of AHEI-2010 score was 0.65 (0.49 to 0.85) (P for trend<0.001; P
for between studies heterogeneity=0.62). When we excluded COPD cases
occurring within the first eight years (n=538), we again observed a
negative association between the AHEI-2010 and the risk of newly
diagnosed COPD: the pooled multivariable hazard ratio for the highest
compared with the lowest fifth of AHEI-2010 score was 0.63 (0.25 to
1.63) (P for trend<0.001; P for between studies heterogeneity=0.65).
Component score of Alternate Healthy Eating Index 2010 and COPD
To
better understand the individual role of each component score of the
AHEI-2010, we examined the association between each individual component
and the risk of COPD (table 5⇓).
High scores on the whole grains and fruit components were associated
with a lower risk of newly diagnosed COPD: 30% (significant) and 19%
(borderline significant), respectively. These associations were similar
among women and men (web appendix 3; P for heterogeneity=0.52 and 0.91,
respectively). For the sugar sweetened drinks and fruit juice component,
the test for heterogeneity was borderline significant (P=0.08); in
women a high score (that is, a low dietary intake close to avoidance)
was associated with a 21% lower risk of newly diagnosed COPD (P for
trend=0.02), whereas in men the association was statistically
non-significant but positive (P for trend=0.06). For the red and
processed meat component, heterogeneity was not significant (P for
between studies heterogeneity=0.10); however, we found no significant
association in women (P for trend=0.22), whereas in men a high score on
the red and processed meat component (that is, a low dietary intake
close to avoidance) was associated with a 53% lower risk of newly
diagnosed COPD (P for trend=0.03). For vegetables, nuts, trans fat,
polyunsaturated fatty acids, long chain fats, sodium, and alcohol, we
found no significant associations with the risk of COPD, and no
significant heterogeneity existed between men and women.
Table 5
Association between each component of Alternate Healthy Eating Index
2010 (AHEI-2010) and risk of newly diagnosed chronic obstructive
pulmonary disease, pooled analysis (Nurses’ Health Study and Health
Professionals Follow-up Study)
Alternate Healthy Eating Index 2010 and asthma
In
the Nurses’ Health Study, 1742 new cases of adult onset asthma were
reported between 1984 and 2000 and met our epidemiologic definition. In
the Health Professionals Follow-up Study, 228 new cases of adult onset
asthma were reported between 1984 and 1998.
Owing to the
potential overlap between COPD and asthma, we also investigated the
association between the AHEI-2010 and the risk of adult onset asthma
(table 6⇓).
In men, in women, and in the pooled analysis, the AHEI-2010 was not
associated with the risk of adult onset asthma: the pooled multivariable
hazard ratio for the highest compared with the lowest fifth of
AHEI-2010 score was 1.04 (0.90 to 1.21).
Table 6
Association between Alternate Healthy Eating Index 2010 (AHEI-2010) and
risk of adult onset of asthma in women (Nurses’ Health Study) and men
(Health Professionals Follow-up Study)
Discussion
In
this prospective cohort analysis of more than 120 000 US women and men,
we found that a higher AHEI-2010 diet score, reflecting high intakes of
whole grains, polyunsaturated fatty acids, nuts, and long chain omega-3
fats and low intakes of red and processed meats, refined grains, and
sugar sweetened drinks, was associated with a lower risk of newly
diagnosed COPD. The association was consistent in several
sub-populations and after adjustment for several potential confounders.
By contrast, the AHEI-2010 diet score was completely unrelated to
incident asthma in this large, prospective cohort analysis. These
findings extend the relevance of this new dietary score to target
chronic diseases and support the importance of diet in the pathogenesis
of COPD. As the lungs exist in a high oxygen environment, it is
reasonable to posit that certain exposures (and local inflammation) can
further increase the burden of oxidants. The balance between these
potentially toxic substances and the protective actions of antioxidant
defenses, including those derived from diet, may play a role in the loss
of lung function over time and the eventual development of COPD.
Comparison with other studies
To
our knowledge, our study is the first to investigate the association
between diet assessed through a priori dietary scores and the risk of
newly diagnosed COPD. Several dietary scores have been proposed in the
literature over the decades since the Mediterranean diet score was
published.24
The diet scores approach is based on prevailing hypotheses and guidance
about the role of nutrients in disease prevention, and the diet is
assessed for compliance with this guidance.9
The other approach to deriving dietary patterns is data driven, with
dietary exposure summarized using statistical techniques. Using this
data driven approach, five studies have investigated the association of
dietary patterns with spirometry or with symptoms or incidence of COPD25 26 27 28 29; we acknowledge that two of these studies included the same participants as our analysis.28 29
Three of the five studies reported a “protective” association for a
“prudent” dietary pattern characterized by a high intake of fruit,
vegetables, fish, and whole grain cereals, consistent with the dietary
antioxidant or anti-inflammatory properties hypothesis. Moreover, four
of the five studies also reported a deleterious role of a “Western” diet
characterized by a high intake of chicken, pork, fish, rice and noodle
dishes, and preserved foods among a population of Chinese Singaporeans27; by a high intake of cured and red meat, potato, boiled vegetables, added fat, coffee, and beer among Dutch adults26;
and by a high intake of cured and red meats, refined grains, desserts,
sweets, French fries, and high fat dairy products among US adults.28 29
Now, in addition to these data driven approaches, we report similar
findings by using a diet score based on foods and nutrients consistently
associated with a lower risk of cardiovascular diseases, diabetes, or
cancer. These findings support the importance of the AHEI-2010 diet
score to also target COPD.
Recent studies have suggested
that COPD patients with multimorbidity represent the norm rather than
the exception and that COPD is just one component of multimorbidity in
patients with COPD.30
Results of epidemiologic studies have shown that COPD is frequently
associated with cardiovascular disease, lung cancer, osteoporosis,
muscle weakness, and cachexia. Mechanistically, environmental risk
factors such as smoking, unhealthy diet, exacerbations, and physical
inactivity or inherent factors such as genetic background and ageing
contribute to these associations.31
When we excluded participants with previous comorbidities (cancer and
cardiovascular diseases), we observed similar associations between the
AHEI-2010 and the risk of COPD, suggesting that a healthy diet may play a
role beyond its association with others chronic diseases.
Sex differences in susceptibility to COPD are probably multifactorial, and many unanswered questions remain.32
With the growing number of female smokers around the world (and the
epidemic of COPD in the female population), a pressing need exists to
answer these and other questions relevant to sex differences in COPD.32
In our study, the number of newly diagnosed COPD cases was twice as
high in women as in men, but women were also twice as likely as men to
be current smokers. Food choices are also an area in which research has
shown consistent behavioral sex differences. Studies conducted in modern
Western societies report consistent associations between sex and choice
of specific foods; for example, meat, alcohol, and hearty portion sizes
are associated with masculinity, whereas vegetables, fruit, fish, and
sour dairy products are associated with femininity.33
We found similar associations among men and women, but statistical
power was lower among men owing to the relatively limited number of COPD
cases in men.
Strengths and limitations of study
Our
study has a few potential limitations. Firstly, newly diagnosed COPD
was defined by a self reported physician’s diagnosis of COPD, and lung
function measures were not available for these large national cohorts.
However, our questionnaire based definition of newly diagnosed COPD was
validated in a subset of registered nurses,21
and we are confident that the accuracy of reporting also extends to the
male health professionals. The main source of disease misclassification
is probably misdiagnosis of asthma. Women who had a high dietary score
and who developed COPD may have preferentially been diagnosed as having
adult onset asthma, a potential bias that would create the appearance of
an association between AHEI-2010 and COPD. However, our findings for
AHEI-2010 and asthma were completely null, which suggests that
misdiagnosis with asthma is an unlikely explanation. We also acknowledge
that misclassification of AHEI-2010 assessed by the food frequency
questionnaire intake is likely. Although we acknowledge the potential
for some misclassification, these data allowed us to investigate the
relations between diet and COPD in a very large sample, with repeated
assessments of both diet and newly diagnosed COPD. Furthermore, this
AHEI-2010 dietary score predicts other chronic diseases in the same
cohorts.12
Secondly, we acknowledge that the association between AHEI-2010 and
COPD may be due, in part, to a residual confounding by cigarette
smoking, which is a powerful risk factor. To minimize this possibility,
multivariable models were adjusted with multiple time varying measures
of tobacco exposure (smoking habits, pack years, and pack years2),
which were assessed biennially from 1976, and analyses were stratified
according to smoking status. An inverse association between AHEI-2010
and risk of COPD remained even after we controlled for all of these
factors, and analyses in ex-smokers yielded comparable results.
Regarding statistics and our models, we acknowledge a possible effect
size of the sample, and even though we controlled for several potential
and known cofounders, our results might still be explained by some
leftover confounding as well as by other healthy lifestyle factors.
Finally, even though our cohorts consisted of female and male health
professionals (that is, a relatively homogenous group as regards
education level), residual differences in socioeconomic status might
have contributed to the observed results.
We also
recognize that our results obtained among health professionals are not
necessarily generalizable to the whole population, as differences in
health awareness, socioeconomic status, and smoking behavior might
differ significantly between the general population and our study
population. Lastly, our study population was mainly non-Hispanic white,
which might limit generalizability of our results to other racial/ethnic
populations. We encourage replication of our prospective findings on
AHEI-2010 and COPD in other populations.
Conclusions and policy implications
In
summary, a high AHEI-2010 dietary score was associated with a lower
risk of newly diagnosed COPD, a novel finding that supports the
importance of diet in the pathogenesis of COPD. This finding extends the
relevance of the AHEI-2010 dietary score to another major chronic
disease, COPD. Although efforts to prevent COPD should continue to focus
on smoking cessation, these prospective findings support the importance
of a healthy diet in multi-interventional programs to prevent COPD. Our
results encourage clinicians to consider the potential role of the
combined effect of foods in a healthy diet in promoting lung health.
Although a single study is unlikely to change clinical practice, our
paper provides further support for non-traditional risk factors for
COPD.
What is already known on this topic
- The Alternate Healthy Eating Index 2010 (AHEI-2010), a new measure of diet quality based on current scientific knowledge, has been linked to risk of major chronic diseases, such as cardiovascular disease, diabetes, and cancer
- The role of dietary scores in risk of chronic obstructive pulmonary disease (COPD) is unknown
- Previous studies have found a lower risk of COPD associated with increased intake of antioxidants and a greater risk of COPD associated with increased intake of processed meats
What this study adds
- A high AHEI-2010 diet score (reflecting high intakes of whole grains, polyunsaturated fatty acids, nuts, and long chain omega-3 fats and low intakes of red/processed meats, refined grains, and sugar sweetened drinks) was associated with a lower risk of COPD
- This finding supports the importance of a healthy diet in multi-interventional programs to prevent COPD
- Regarding public health, this finding extends the relevance of the AHEI-2010 dietary score to another chronic disease, COPD
Notes
Cite this as: BMJ 2015;350:h286
Footnotes
- We thank Gary Chase and Karen Corsano for invaluable assistance with the implementation of the study. We also thank Marjory McCullough, Rong Chen, and Rui Jiang for their help with the dataset.
- Contributors: RV conceived the study, collected the data, planned and performed the statistical analysis, and drafted and critically revised the manuscript. SEC and TTF conceived the study, planned the analysis, and critically revised the manuscript. RGB, FBH, WCW, and CAC conceived the study, collected the data, obtained funding, planned the analysis, and critically revised the manuscript. All authors approved the final version for publication. RV and CAC are the guarantors.
- Funding: This study was supported by grants CA-87969, CA-167552, HL-63841, and AI-52338 from the National Institutes of Health (Bethesda, MD, USA). The design, conduct, and reporting were entirely the responsibility of the authors, independent from funders.
- Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: no support from any organization for the submitted work; no financial relationships with any organizations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.
- Ethical approval: The institutional review board approved the Nurses’ Health Study and the Health Professionals Follow-up Study protocols, and all participants gave written consent. The study was conducted according to the ethical guidelines of Brigham and Women’s Hospital (Boston, USA).
- Transparency declaration: The lead author (the manuscript’s guarantor) affirms that the manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.
- Data sharing: Requests for access to data, statistical code, questionnaires, and technical processes may be made by contacting the corresponding author at raphaelle.varraso@inserm.fr.
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