Black women who consumed the highest amounts of dairy products - two servings a day - and around six portions of fruits and vegetables had at least a 30 per cent lower risk of disability than participants who consumed the lowest amounts of these foods, shows the research, published in this month's issue of the American Journal of Clinical Nutrition (vol 81, issue 2, pp515-522).
Among all participants, eating more of these foods was associated with lower risk for functional limitations, such as being unable to walk a quarter of a mile or climb 10 steps, that often precede disability, said the team from Wake Forest University Baptist Medical Center.
"Getting the recommended number of servings of dairy, fruits and vegetables should be investigated for its potential to reduce the prevalence of disability in the ageing population," said study author Denise Houston.
The findings are important because the number of disabled elderly is expected to surge with the rise of ageing populations, made worse by the increasing tendency to be obese.
In the US, researchers have forecast that disabled elderly will triple between 1985 and 2050. About half of people over age 65 will become disabled enough to require some nursing home care.
"We know that obesity, lack of physical exercise, alcohol consumption and smoking are modifiable risk factors for disability, but little is known about the role of diet," said Houston.
The researchers believe this is the first study to report on an association between disability and eating certain foods.
It is not clear why these foods could decrease the risk of disability but Houston suggests that the calcium and vitamin D in dairy foods may decrease the risk of disability associated with osteoporosis and decreased muscle strength.
Also the antioxidants found in fruits and vegetables may reduce the accumulation of oxidative damage in tissues, which could slow disability associated with ageing and decrease the risk of chronic diseases that can lead to disability.
The study is based on data from the Atherosclerosis Risk in Communities (ARIC) trial, which included about 16,000 participants. People aged between 45 and 64 years old when the study began were asked to report on their diets over the past year using a 66-item food frequency questionnaire.
After an average of nine years, the researchers surveyed participants on their ability to perform 12 daily activities, such as dressing and feeding themselves and walking across a room, known as activities of daily living; being able to cook and manage their money, known as instrumental activities of daily living; and being able to walk a quarter of mile and walk up 10 steps without resting, to measure functional limitations.
The study adjusted for other factors that could have affected the results -age, education, smoking, and body mass index - and found that higher amounts of dairy (two servings a day), fruits and vegetables (on average three of each daily) were associated with lower risk of functional limitations.
Among black women, risk of disability was significantly lower.
The study offers further support for public health messages campaigning for consumption of 'five-a-day' fruits and vegetables.
The median servings for participants consuming the lowest amounts of the foods were less than half a serving of dairy and one or less serving of fruits and vegetables.