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What is the ideal dietary requirement for Vitamin D in healthy adults?
Editor's note: Estimates of the ideal dietary requirement for Vitamin D in healthy adults varies widely, and few reports note the significance of sun exposure relative to dietary intake. A number of studies suggest that while most have sufficient vitamin D intake to prevent rickets and osteomalcia, current cutoff levels may still place individuals at risk for other disease. This is a great study for those interested in learning more about this significant clinical topic!
This recent, randomized, placebo controlled, double blind study was aimed at assessing the
distribution of dietary vitamin D intakes required to maintain serum 25-hydroxyvitamin D [25(OH)D] concentrations above
several proposed cutoffs. While vitamin D is primarily obtained through dermal synthesis in the presence of sun exposure,
dietary vitamin D becomes essential in winter months or in cases of low exposure to sunlight. This study is timely, as the
authors note that threshold levels for vitamin D adequacy are widely disputed among authoritative bodies in the US, UK and European Union.
Historically, it is well established that serum concentrations of 25(OH)D of <10-25 nmol/L leads to rickets in children and osteomalcia in adults.
While the lower recommended threshold of vitamin D status in the UK is 25 nmol
25(OH)D/L (sufficient to prevent rickets and osteomalcia) researchers note that a growing body of
evidence links an increased risk of a number of nonskeletal chronic diseases with serum 25(OH)D concentrations < 50nmol/L.
221 men and women aged 20-40 y from Northern Ireland completed this 22-wk intervention trial
between October 2006 and April 2007. Volunteers were excluded if they consumed vitamin D
supplements three months prior to the study or planned to take a
winter vacation during the study period. Vitamin D3 capsules and matching placebo capsules were distributed following randomization and adjustment
for age (20-30 or >30-40) and sex. Because
vitamin D is largely acquired via dermal synthesis, the researchers sought to design a study that would identify intake values that
would maintain serum 25(OH)D concentrations above established cutoffs when dermal synthesis is significantly decreased or absent.
Cashman et al “found that a daily intake of 8.7 ug vitaminD/d would have maintained serum 25(OH)D concentrations >25nmol/L in 97.% of the sample. They went on to report
that “because the thresholds for vitamin D adequacy are widely disputed, we also reported the 50th, 90th, 95th, and 97.5th percentiles of vitamin D intakes required to maintain serum 25(OH)D concentrations in excess of 37.5, 50, and 80 nmol/L; which for 97.5% was 19.9, 28.0 and 41.1 ug, respectively." With regard to the vitamin D intake needed to maintain concentrations of 25(OH)D >25 nmol/L subjects who self-identified as sun avoiders needed an additional of 5.1 ug of vitamin D compared to those whose identified as enjoying the sun. These findings, assert researchers, may contribute essential data for reestablishing an RNI for vitamin D to be used in devising nutrition policy among the many
authoritative bodies responsible throughout developed countries.
Study: Cashman, K., et al, Am J Clin Nutr, 88: 1535-42 (2008) Return to Home from vitamin d dietary requirement study |
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