Journal Watch General Medicine<br>April 23, 2009

Vitamin D Levels in Elders

Allan S. Brett, MD

Disclosures

Journal Watch. 2009;8(4) 

Most older people had low serum levels, and at least 25% of elders had frank vitamin D deficiency.

Two studies in the Journal of Clinical Endocrinology and Metabolism focus on vitamin D in older populations.

Researchers measured serum 25-hydroxyvitamin D (25[OH]D) in 6000 community-dwelling men (age range, 65--99) who lived in various U.S. regions. Average serum 25(OH)D level was 25 ng/mL; one quarter of subjects had levels lower than 20 ng/mL. In multivariable analysis, lower 25(OH)D levels were associated with older age, obesity, black or Latino ethnicity, blood sampling in winter, and residence at a northern latitude (e.g., Minneapolis, compared with San Diego). Use of vitamin D supplements and engaging in outdoor activities were associated with higher vitamin D levels.

Dutch researchers examined relations between vitamin D levels and bone metabolism in 1300 randomly selected older adults (age range, 65--88). Mean serum 25(OH)D level was 21 ng/mL; half the participants had levels lower than 20 ng/mL. Findings included the following:

  • Serum parathyroid hormone levels were inversely proportional to vitamin D levels, without any plateau effect.

  • Markers of bone turnover (serum osteocalcin and urinary deoxypyridinoline) were inversely proportional to 25(OH)D levels until the latter exceeded 20 ng/mL; above that point, bone turnover markers plateaued.

  • Total hip bone-mineral density was directly proportional to 25(OH)D levels until the latter exceeded 20 ng/mL; above that point, bone density plateaued.

Comment

Average vitamin D levels were similar in both of these studies in older people. The factors that predisposed elders to vitamin D deficiency in the U.S. study have been recognized previously in younger populations. The Dutch results suggest that bone metabolism is affected adversely when 25(OH)D levels drop below a threshold of about 20 ng/mL. This finding supports 20 ng/mL as a reasonable cutoff for a designation of vitamin D deficiency.


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