Vitamin D = placebo for preventing cognitive decline in African-American women with low vitamin D levels

Référence

Owusu JE, Islam S, Katumuluwa SS, et al. Cognition and vitamin D in older African-American women—physical performance and osteoporosis prevention with vitamin D in older African Americans trial and dementia. J Am Geriatr Soc 2019;67(1):81-86.

Sommaire

These authors recruited African-American women from various community settings. During a pre-enrollment telephone interview, women were asked not to take vitamin D–containing supplements for 4 to 6 weeks before the study. The researchers then measured their serum vitamin D levels and included those women with levels between 8 ng/mL and 26 ng/mL. They excluded women with hip osteoporosis, Mini-Mental State Examination (MMSE) scores of less than 21, moderate to severe vertebral fractures, liver disease, or kidney stones. The researchers randomly assigned half the women to receive daily vitamin D3 (2400 IU, 3600 IU, or 4800 IU); n = 130) and the other half to receive matching placebo (n = 130). They used the baseline vitamin D level to determine the initial dose, then titrated the dose every 3 months to achieve a target level of 30 ng/mL. They also gave women in each group 1200 mg calcium daily. The researchers assessed the MMSE score every 6 months for 3 years and used a score of less than 27 as the cutoff for mild cognitive impairment. Unfortunately, 74 women dropped out of the study, which raises serious concerns about trusting the final results. Among the women who completed the study, the MMSE scores increased in both groups and the degree of improvement was comparable. The authors report no vitamin D–related adverse events. The authors, unfortunately, don't provide sample size or power estimates for the study. Finally, they properly recognize the limitations of the MMSE in detecting cognitive decline.