Study Overview
Objective. To evaluate the contribution of dietary habits in midlife on healthy aging.
Study design. Observational investigation of an ongoing cohort study.
Setting and participants . Participants were gathered from the Nurses’ Health Study, a cohort of 121,700 married female nurses who have completed health-related questionnaires every 2 years since 1976. Data on race was not originally collected, but a subsample analysis revealed that the cohort of nurses was > 98% white [1]. A subset of this cohort ( n = 19,415) older than age 70 years from 1995 and 2002 and who received additional cognitive testing was chosen as the population of interest for this study. The investigators excluded participants with missing data ( n = 5878) on important covariates and participants who had any of 11 chronic diseases in midlife ( n = 2585), obtained from questionnaires in the 1980s. 10,670 participants were included in the final analysis.
Main outcome measures. Participants were dichotomized as “healthy agers” or “usual agers” on the basis of 4 health domains measured in 2000. Persons free of 11 chronic diseases, without cognitive impairment, without physical limitations, and with intact mental health were designated “healthy agers,” with the remainder designated “usual agers.” For each domain, specific criteria were employed to indicate impairment. Cognitive impairment was defined as a score of 31 or greater on the Telephone Interview for Cognitive Status. Investigators used the Medical Outcomes Short-Form 36 health survey (SF-36) to measure physical impairment and mental health. Participants who reported being limited at least “a little” on moderate activities or limited “a lot” on strenuous activities were classified as physically impaired. Intact mental health was defined as a score above the cohort’s median on the mental health subscale of the SF-36.
Dietary habits were ascertained at midlife by an average of the 1984 and 1986 food frequency questionnaire (FFQ) data. Using these data, the authors calculated the Alternative Healthy Eating-2010 (AHEI-2010) and the Alternate Mediterranean Diet (A-MeDi) scores. AHEH-2010 incorporates the latest knowledge on the benefits and harms of foods and nutrients on the risk of chronic disease. It has 11 domains (including whole grain intake, vegetable intake, and lower intake of trans fats, among others) which are each scored 0 (worst) to 10 (best). The A-MeDi score assesses adherence to the traditional Mediterranean diet, which includes intake of vegetables, fruits, nuts, legumes, and moderate alcohol intake, among others. Each of 9 categories is rated 0 or 1, with 1 representing healthy intake.
Covariates included sociodemographic, lifestyle, and health-related measures obtained either in 1984 or 1986. These included age; educational level; household income and home value estimated from census tract data; marital status; family history of diabetes, cancer, and myocardial infarction; physical activity; smoking; multivitamin and aspirin use; BMI; history of high blood pressure; and hypercholesterolemia. BMI was obtained via self-report and averaged from among values obtained in 1984 and 1986; these have previously been shown to have excellent correlation ( r = 0.97) to standardized examinations [2].
The authors standardized baseline characteristics for each study participant based upon the age at which they entered the study. They used logistic regression to estimate the odds of being a “healthy ager” in the year 2000 by quintile of AHEI-2010 and A-MeDi scores.
Main results . Of the 10,670 participants, 1171 (11%) were labeled “healthy agers” and 9499 (89%) were labeled “usual agers.” Prevalence in each of the 4 health domains varied widely: 9599 (90%) of the 10670 participants had no cognitive impairment, 7234 (67.8%) had no chronic diseases, 4606 (43.2%) had no mental health limitations, and 2905 (27.2%) had no impairment of physical functioning.
Investigators presented data comparing healthy agers and usual agers at baseline without tests for significance. The mean age of healthy agers and usual agers was comparable (58.6 [SD = 2.5] vs. 59.1 [SD = 2.5]). Healthy agers had lower prevalence of obesity (3% vs. 13%), ever smoking (54% vs. 47%), higher mean physical activity (19.4 MET h/wk [SD = 21.7] vs. 14.1 MET h/wk [SD = 19.8]), lower energy intake (1692 kcal/d [SD = 472] vs. 1743 kcal/d [SD = 477]) and lower prevalence of hypertension (20% vs. 32%) and hypercholesterolemia (12% vs. 17%). Healthy agers also had higher baseline AHEI-2010 (53.2 [SD = 10.3] vs. 50.6 [SD = 10.1]) and A-MeDi scores in midlife (4.5 [SD = 1.6] vs. 4.3 [SD = 1.7]).
Greater scores on the AHEI-2010 and A-MeDi measures in midlife were associated with greater odds of healthy aging in multivariate analysis. After adjusting for all covariates, women in the highest quintile of AHEI-2010 scores at baseline had 34% greater odds (95% CI, 9% to 66%) of being healthy agers compared to women in the lowest quintile. Likewise, adjusted analyses reported women in the highest quintile of A-MeDi scores had 46% greater odds (95% CI, 17% to 83%) of being healthy agers.
Secondary analyses tested each component of healthy aging for associations with AHEI-2010 and A-MeDi scores in midlife. Associations were overall weaker, but no impairment of physical function and no limitation of mental health were both found to be significant after adjustment for covariates. Women in the highest quintile of AHEI-2010 scores at baseline had 23% (95% CI, 11% to 36%) and 13% (95% CI, 5% to 22%) greater odds, respectively, of not having any physical limitations or mental health impairments in late life compared to women in the lowest quintile. Likewise, women in the highest quintile of A-MeDi scores at baseline had 14% (95% CI, 3% to 26%) and 12% (95% CI, 4% to 20%) greater odds, respectively, of not having any physical limitations or mental health impairments in late life compared to women in the lowest quintile.
The authors also tested the effect of individual components of dietary patterns on healthy aging, comparing those in the highest quintile versus those in the lowest quintile for each measure. Persons with the greatest intake of fruits had 46% (95% CI, 15% to 85%) greater odds of being healthy agers compared to those with the lowest intake of fruits. Persons with the highest intake of alcohol had 28% greater odds (95% CI, 4% to 56%) of being healthy agers compared to those with the lowest intake of alcohol. Conversely, those with lower intake of sugar-sweetened beverages (OR, 1.28 [95% CI, 1.03 to 1.58]) and non-omega 3 polyunsaturated fatty acids (OR, 1.38 [CI, 1.10 to 1.73]) had better odds of being healthy agers compared to those with higher intakes.
Conclusion. Women with healthy dietary patterns at midlife had significantly greater odds of being healthy agers in later life after adjusting for potential con-founders. Results were consistent in direction and effect size when using either the AHEI-2010 score or the A-MeDi score. The effects of healthy diet at midlife seemed to have the strongest association with physical impairment scores and mental health scores. Higher intake of fruits and alcohol along with lower intake of sugar-sweetened beverages and polyunsaturated fatty acids seemed to have the most power for predicting healthy aging.
Commentary
These results are consistent with current knowledge, which indicates the health benefits of a balanced, healthy diet high in fruits, vegetables, whole grains, nuts, and legumes and low in red or other processed meats. There is high quality evidence linking each dietary measure to health outcomes. Adherence to the Alternative Healthy Eating Index has been related to lower mortality rates [3], decreased risk of cardiovascular disease [4], and decreased risk of type 2 diabetes and the metabolic syndrome [5]. Likewise, adherence to the Mediterranean diet is associated with reductions in overall mortality, cardiovascular incidence and mortality, cancer incidence and mortality, and neurodegenerative diseases [6]. Both diets endorse moderate alcohol intake, which was associated with lower rates of all-cause and cardiovascular mortality in a meta-analysis [7]. Alcohol is theorized to produce decreased platelet aggregation, increase HDL cholesterol, and increase endothelial vasorelaxation [8]. Polyphenols, most prominent in red wines, may have additional effects which include vaso-relaxation of aortic rings, reduced thrombosis and inflammation, and increased fibrinolysis [9]. Nevertheless, heavy alcohol use may increase cardiovascular mortality, hypertension, and hyperlipidemia [8]. This study concluded that higher alcohol intake was related to being a healthy ager; this may be because there are few heavy alcohol users in this cohort, though this hypothesis was not tested in the study.
Any observational study is subject to debate about the confounders chosen for analysis and potential biases. The authors report that the most powerful confounders in this analysis were BMI, physical activity, and smoking, all of which have been well established as predictors for health in later life [10]. Nonetheless, important potential confounders not used in analysis included the baseline prevalence of mental health problems, cognitive limitations, and physical limitations, all of which were not available.
The greatest concern about of this study is a potential lack of generalizability given the population surveyed. The Nurses’ Health Study consists of a cohort of female, married, predominantly white registered nurses [1]. For instance, African Americans have a greater burden of hypertension than non-Hispanic whites after accounting for dietary differences [11], a higher degree of late-life cognitive dysfunction [12], and greater risk of developing late-life physical disability [13]. Also, race and ethnicity may impact eating patterns, food preferences, and food availability in ways that are difficult to predict. In addition, nurses in the cohort were probably of similar socioeconomic status given their shared occupation, though the authors did not report the variation in median household incomes obtained from census tract analysis in this study [14]. Results might change if the sample was less homogeneous. Nonetheless, the results are consistent with current knowledge, biologically plausible, and clinically meaningful.
Applications for Clinical Practice
Integrating dietary changes in middle-aged women may be an important means of decreasing morbidity in older age and improving physical and mental health functioning later in life. Health care providers should discuss the future benefits of healthy eating on quality of life in order to encourage patients in midlife to alter their diet in meaningful ways. While it may be difficult to generalize these findings to patients of different genders, races, or ethnicities, the biological underpinnings of the data make it hard dispute the conclusions presented in the study.
—Hector Perez, MD, and Melanie Jay, MD, MS