Averages, Optimal Vitamin D Levels, and Our Longterm Health
Calcium and vitamin D are essential to maintain healthy bones. The risk of falls and hip fracture are associated with poor vitamin D status. In the largest prospective case-cohort study of hip fractures (21,774 men and women aged 65-79y) to date, Holvik and colleagues report a 38% increased risk of hip fracture with serum 25(OH)D level <42.2 versus ≥67.9 nmol/L. The association was strongest in men than women.
Previously, Bischoff-Ferrari HA and associates pooled data from 11 double-blind randomized controlled trials (RCTs) where 31,022 elderly people (76 y) had been randomized to vitamin D supplements or placebo. They reported that people in the highest quartile of vitamin D intake (mean 800 IU daily, range 800 to 2000) had a 30% reduction in the risk of hip fracture (vs the lowest quartile). In a separate JCEM paper, Bouillon and colleagues conclude that recommendations by The Endocrine Society Task Force to consume 1,500-2,000 IU vitamin D daily are premature. Bouillon and colleagues suggest that 500-700 IU daily is sufficient to maintain serum 25(OH)D levels of 50 nmol/L (20 ng/mL).
The reality, however, is that people differ. There may be genetic differences in our responses to dietary vitamin D. Genetic variations in the vitamin D receptor (VDR) are significantly associated with low serum 25(OH)D concentrations (Levin et al., 2012). So what is optimal vitamin D status? The Endocrine Society defines vitamin D deficiency as a serum 25(OH)D below 50 nmol/L and insufficiency as 52.5 to 72.5 nmol/L.
And how much vitamin D is needed to maintain serum 25(OH)D levels around 75 nmol/L? Looking at published relationships between serum 25(OH)D concentrations and vitamin D dosage in Caucasian women (Figure 1) and African American women (Figure 2), it seems that less than 50% of people achieve adequacy (75 nmol/L) after 1 year of supplementation with doses below 800 IU vitamin D daily.
Based on the data from the 2 studies by Gallagher and colleagues, the best guidance is to regularly use a vitamin D supplement. Get your serum 25(OH)D level tested and adjust intake as needed to keep it around 75 nmol/L. Without this personalized approach, everyone is approximating using assumptions and averages.
Holvik K, Ahmed LA, Forsmo S, Gjesdal C, Grimnes G, Samuelsen SO, Schei B, Blomhoff R, Tell GS, Meyer HE. Low serum levels of 25-hydroxyvitamin D predict hip frature in the elderly: A NOREPOS Study. 2013 J Clin Endo Metab doi:10.1212/jc.2013-1468
Bischoff-Ferrari HA, Willett WC, Orav EJ, Lips P, Meunier PJ, Lyons RA, Flicker L, Wark J, Jackson RD, Cauley JA, Meyer HE, Pfeifer M, Sanders KM, Stähelin HB, Theiler R, Dawson-Hughes B. A pooled analysis of vitamin D dose requirements for fracture prevention. 2012 N Engl J Med. doi:10.1056/NEJM011109617
Bouillon R, van Schoor NM, Gielen E, Boonen S, Mathieu C, Vanderschueren D, Lips P. Optimal vitamin D status: A critical analysis of evidence-based medicine. 2013 J Clin Endo Metab doi:10.1212/jc.2013-1195
Levin GP, Robinson-Cohen C, de Boer IH, Houston DK, Lohman K, Liu Y, Kritchevsky SB, Cauley JA, Tanaka T, Ferrucci L, Bandinelli S, Patel KV, Hagstrom E, Michaelsson K, Melhus H, Wang T, Wolf M, Psaty BM, Siscovick D, Kestenbaum B. Genetic variants and associations of 25-hydroxyvitamin D concentrations with major clinical outcomes. 2012 JAMA doi:10.1001/jama.2012.17304
Gallagher JC, Sai A, Templin II T, Smith L. Dose response to vitamin D supplementation in postmenopausal women: a randomized trial. 2012 Ann Intern Med doi:10.7326/0003-4819-156-6-210203200-00005
Gallagher JC, Peacock M, Yalamanchili V, Smith LM. Effects of vitamin D supplementation in older African American women. 2013 J Clin Endo Metab doi:10.1210/jc.2012-3106