The study, published in November's Archives of Internal Medicine, involved 643 women aged 65 years or older. The women were assessed at six-month intervals between 1992 and 1995, and subsequently followed-up for three years.
The link between low nutrient levels and difficulty in performing daily activities is relevant for the quality of life and health care expense issues surrounding the aging baby boomer generation, who by 2030 will all be older than 60.
Currently, approximately seven million people over the age of 65 in the US are disabled. But, with baby boomers accounting for nearly 30 percent of the American population and inching closer to 65, this looks set to rise dramatically. Catering to this age group is a major focus for the nutritional products industry.
The study, entitled "Low micronutrient levels as a predictor of incident disability in older women", defined disability in activities of daily living as self-reported difficulty in performing two or more activities such as bathing, dressing, toileting, transferring and eating.
The Cornell researchers emphasized that their findings do not provide basis for supplementation as a means to prevent such disability. Instead, they uphold the generalization that nutritional status on the whole facilitates improved mobility.
Of the women who did not already have a daily living activity disability at the beginning of the study, 208 (32.3 percent) developed two or more during the three-year follow-up period. The women in the lowest quartile of serum concentrations of vitamin B6 and B12, as well as selenium had a significantly higher risk of disability during the three years, when compared with women in the upper three quartiles.
The incidence rate in the lowest quartile for vitamin B6 was 17.3 percent, compared with 12.8 percent for the upper three quartiles. For vitamin B12, rates of incidence were 16.7 percent in the lowest quartile and 12.0 percent in the three highest. And for selenium the results were 21.6 percent and 10.8 percent respectively.
Selenium prevents cellular damage through selenoprotein antioxidant enzymes.
"Low antioxidants may tip the balance between antioxidants and free radicals and allow increased oxidative stress," wrote the authors. "This imbalance may lead to disability through dysregulation of cellular function and up-regulation of proinflammatory cytokines, muscle and neuronal damage, and the exacerbation of degenerative diseases."
Deficiencies in vitamins B6 and B12 cause hyperhomocysteinemia.
"The association of high levels of homocysteine with oxidative stress, endothelial dysfunction, occlusive vascular diseases, and, in particular, with decline of cognitive function may explain, at least in part, our findings on the association of low concentrations of B6 and B12 with disability," wrote the authors.
Bartali, Benedetta et al. "Low micronutrient levels as a predictor of incident disability in older women." Archives of Internal Medicine. 2006; 166:2335-2340.