To the Editor: Dr Bartali and colleagues1 performed a longitudinal study of serum micronutrients and physical decline in older persons. Although they found an association between low serum concentrations of vitamin E and physical decline, the study had a large dropout rate, and we are concerned about the potential for selection bias.
The authors report that, compared with those assessed, the 457 excluded participants (39.6% of total participants) were significantly older and had lower physical activity levels, poorer cognitive and physical function, and lower vitamin D levels, but they do not provide any information about vitamin E serum concentration (the characteristic of most interest). It would be important to know if this level were higher in the excluded group.
Krul M, Damen J, vander Wouden JC. Vitamin E Concentration and Physical Decline in Older Persons. JAMA. 2008;299(17):2021. doi:10.1001/jama.299.17.2021-a