Short Limbs Associated with Risk of Dementias

By Todd Neale
BOSTON, 06 may 2008 -- A man with a 32-inch sleeve has a greater risk of developing Alzheimer's disease and other dementias than a man with a 35-inch sleeve.
So it seems from a prospective, longitudinal study showing that for both men and women, having shorter limbs is associated with increased risks for Alzheimer's and other dementias.
Women in the lowest quartile of arm span had a 1.42-fold greater risk of dementia and a 1.72-fold increased risk of Alzheimer's disease compared with other women, reported Tina Huang, Ph.D., of the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts, and colleagues in the May 6 issue of Neurology.
Every one-inch increase in knee height in women was associated with a 16% lower risk of dementia and a 22% reduced risk of Alzheimer's disease.
For men, every one-inch increase in arm length was associated with a lowering of the risk of dementia by 6% and the risk of Alzheimer's by 7%, they said.
"Our findings with knee height and arm span are consistent with previous reports and suggest early life environment may play an important role in the determination of future dementia risk," they said.
Anthropometric measures can be used as markers of childhood environment, and may reflect nutritional or other deficits during early development, the researchers said.
Several studies have linked early environmental factors and susceptibility to disease in later life, they said, and some, including three on Korean populations, have made the connection between shorter leg and arm lengths and cognitive impairment.
For an American population, Dr. Huang and colleagues turned to the Cardiovascular Health Cognition Study, which followed 2,798 patients (mean age 72; 41% male; 89.5% white) for an average of 5.4 years.
Knee height was measured three years before the study started and arm span was measured four years after baseline.
Cerebral MRI was performed at the start of the study and at five years. Cognitive function was measured at baseline and then at each follow-up visit using the Modified Mini-Mental State Examination.
During follow-up, 480 participants developed dementia for an incidence of 31.9 cases per 1,000 person-years: 245 were possible or probable Alzheimer's disease, 213 were possible or probable vascular dementia, and 22 were other dementias.
The association of a lower risk of dementia and Alzheimer's with greater knee height was only significant in women, after controlling for age, race, and presence of the APOEe4 allele, which is known to increase the risk for dementia and Alzheimer's disease.
For women, every one-inch increase in arm length was associated with a lowering of the risk of dementia by 6% (HR 0.94, 95% CI 0.89 to 0.99) and the risk of Alzheimer's by 9% (HR 0.91, 95% CI 0.85 to 0.97).
"Differences in limb length," the researchers said, "could reflect differences in genetics, environment, or both."
Insufficient nutritional intake during childhood could cause stunted growth, which is reflected in shorter height and limb length, and impaired brain development, they said.
"Thus," they continued, "it is possible that early nutritional deficits, exposure to environmental toxins, or other unaccounted-for residual confounders could influence intelligence, cognitive functioning, level of educational attainment, or vulnerability to dementia."
The authors acknowledged that the study was limited by the measurement of arm length four years after the start of the study and the possibility of misclassification of dementia outcome.
Strengths of the study included the length of follow-up, the longitudinal, prospective design, the "state-of-the-art adjudication of incident dementia, Alzheimer's, and vascular dementias," and the high number of dementia cases.
"These reasons, plus the fact that our studies have now replicated previous findings," they concluded, "increase our confidence in concluding that the shorter a woman's knee height, or the shorter the arm span of either gender, the greater the risk of developing dementia or [Alzheimer's disease]."
They called for further studies to explore gender differences in the associations of knee height and arm span with dementia.
Dr. Huang was supported by grants from the NIH, the National Institute of Diabetes and Digestive and Kidney Diseases, and the Charles A. King Trust, and the U.S. Department of Agriculture Agricultural Research Service. The study was supported by contracts from the National Heart, Lung, and Blood Institute and a grant from the National Institute on Aging.
The authors reported no conflicts of interest.
Primary source: NeurologySource reference:Huang T, et al "Knee height and arm span: a reflection of early life environment and risk of dementia"Neurology 2008; 70: 1818-1826.Additional Dementia Coverage