Are there particular populations of adults for whom you would recommend screening, or vitamin D supplementation in the absence of screening?
Response from David B. Reuben, MD
Professor and Archstone Foundation Endowed Chair, Department of Medicine, University of California Los Angeles; Chief, Division of Geriatrics, UCLA Medical Center, Santa Monica, California
Several prospective epidemiologic studies have shown associations of low serum vitamin D levels with lower global cognition and more rapid functional decline,[1-4] as well as the development of dementia and Alzheimer disease. In a recent review of nine epidemiologic studies, the serum level that was associated with worse cognitive health was found to be around 10 ng/mL. However, such studies cannot determine whether low vitamin D was causal or whether persons with memory problems were less likely to leave their homes and therefore have less sun exposure, leading to lower vitamin levels.
It is less clear whether and how much vitamin D supplementation would improve cognition or prevent decline in older populations. To date, there are no randomized clinical trial data supporting supplementation for improving cognition or preventing decline.
In the Women’s Health Initiative Memory Study, calcium and 400 IU vitamin D3 supplements given to a randomized sample of women did not result in differences in performance (attention, working memory, word knowledge, spatial ability, verbal fluency, verbal memory, figural memory, or fine motor speed) over 7.8 years. Moreover, in observational studies, high levels of 25-hydroxyvitamin D, especially among those taking vitamin D supplements, have been associated with cognitive impairment on a battery of attention tests, suggesting a possible U-shaped curve relationship.
Recently, the US Preventive Services Task Force has reviewed the evidence for screening for vitamin D deficiency and concluded that the current evidence is “insufficient to assess the balance of benefits and harms of screening for vitamin D deficiency in asymptomatic adults.” Part of the rationale for this recommendation stemmed from the paucity of studies that used an internationally recognized reference standard and the lack of consensus on the laboratory values that define vitamin D deficiency.
In summary, the best evidence supports the recommendation of daily dietary vitamin D intake of 600 IU in adults aged 18-70 years and 800 IU in adults older than 70 years (1000 IU is commonly marketed). Vitamin D levels should be obtained in patients with symptoms of osteomalacia (eg, diffuse bone and joint pain, fractures, muscle weakness, and difficulty walking), especially in malabsorption states, and before starting intravenous bisphosphonate therapy for osteoporosis because of the potential for precipitating hypocalcemia in patients with hypovitaminosis D receiving these medications. Currently, there is no indication for screening asymptomatic patients for vitamin D levels for the purpose of potentially supplementing with vitamin D in order to prevent changes in cognitive outcomes.