Archief Roodbont

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.

— Allan S. Brett, MD

Published in Journal Watch General Medicine April 23, 2009