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Can a good diet help prevent disability in later life?
(February 2006)

Investigators from the University of North Carolina recruited 9,400 men and women ages 45 to 65 years from four “representative communities around the United States”. At entry, intake of dairy products, fruits, and vegetables was determined. Then they were followed for nine years. Three types of disability were analyzed - lower limb mobility, mild disabilities (doing chores around the house, preparing meals, managing money), more severe disabilities (walking from one room to another, getting in or out of bed, eating or drinking from a glass, dressing oneself). Participants were divided into three dietary intake groups for dairy foods and drinks, fruits, and vegetables - low, medium, and high.

The results varied by participant group. For black women, higher dairy food and fruit intakes markedly reduced disabilities and higher vegetable intake had a lesser beneficial effect. White women who had high intake of dairy foods and fruits showed modest reduction in disabilities. Black men with high dairy intake had reduced disabilities; additionally, there may have been some benefit from high intake of fruits. Overall, the reduced disability risk for black women was quite marked, whereas it was less impressive for white women and black men. White men showed no consistent benefits. Dairy foods and fruits were associated with reduced disability risk; vegetables, in general, were not.

Commentary: It is hard to accept that getting a good calcium intake or eating a lot of fruit reduces moderate to marked disabilities during subsequent aging. But, the paper is important because it begins to focus on a critical problem, namely what we can do in early adulthood, middle age, or even as we get older than that to reduce moderate or severe disabilities that affect the quality of life and often cost the health care system a lot of money. Diet may turn out to be important, but there are several substantial issues with this study.

- The authors say they took into account physical activity, but they provide no specific evidence and it is likely they did not look at physical activity during the nine-year followup period when the disabilities occurred.

- The investigators did take Body Mass Index (weight in kilograms divided by square of the height in meters) into account. That is a critical variable, but they did not apparently look at change in Body Mass Index or weight gain during the followup period. That is a big issue.

- This is a somewhat unusual group. They averaged 53 years of age at enrollment; yet only nine years later, the percentage with moderate to severe disability seems to be greater than would be expected in the general population in this age category. An occurrence of disability was particularly high among black women, the group in which dairy food and fruit intake had the greatest effect. Among those women, 22 percent reported severe disabilities and 30 percent moderate disabilities. Those percentages are hard to believe in persons with an average age at followup of 63 years.

- In different groups, 37 to 67 percent had impaired leg function at followup, but the definition of lower extremity dysfunction used was so broad, it is unclear that they were really measuring lower leg function (the definition included: walking up ten steps without resting, stooping or crouching; lifting an object weighing at least ten pounds; walking one-quarter mile; and standing up from an armless straight back chair).

So, the subject is important and this is a perfectly good start, but do not take the conclusions too seriously, and the diet may not be the critical variable, but rather the healthier diet may be a surrogate for some other health-promoting behaviors that may account for the benefit.

The rating is not meant to disparage the study; rather, it is to indicate we need many more such studies before drawing any conclusions. And, despite the reservations, diet could turn out to be quite important.

Houston, D.K., et al. Dairy, fruit and vegetable intakes and functional limitations and disability in a biracial cohort. American Journal of Clinical Nutrition. Vol 81 Pgs 515-522. 2005.

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