A new position statement by the foundation, published in Osteoporosis International, examined all available evidence to support new recommendations for optimal vitamin D status, and found that older adults should consume between 800 and 1,000 International Units (IU) per day in order to ensure sufficient blood levels of the vitamin.
“Global vitamin D status shows widespread insufficiency and deficiency,” said the statement’s lead author Professor Bess Dawson-Hughes of Tufts University. “This high prevalence of suboptimal levels raises the possibility that many falls and fractures can be prevented with vitamin D supplementation. This is a relatively easy public health measure that could have significant positive effects on the incidence of osteoporotic fractures.”
The lowdown on D
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former is produced in the skin on exposure to UVB radiation (290 to 320 nm). The latter is derived from plants and only enters the body via the diet.
Both D3 and D2 precursors are hydroxylated in the liver and kidneys to form 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that is tightly controlled by the body.
Vitamin D deficiency in adults is reported to precipitate or exacerbate osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases. There is also some evidence that the vitamin may reduce the incidence of several types of cancer and type-1 diabetes.
The science supporting the muscle function of vitamin D, as well as the vitamin’s role in immune health, is sufficiently robust to have merited a positive opinion from the European Food Safety Authority’s (EFSA) Panel on Dietetic Products, Nutrition and Allergies (NDA).
The new statement from the IOF echoes other calls for increases in the daily recommended intake levels. The influential Institute of Medicine (IOM) in the US is conducting a review of the available vitamin D science and is due to deliver its findings this summer. Many expect the IOM to recommend RDIs much above the current levels of 400 IU. Oprah has been telling her viewers the RDI should be 2,000 IU or more.
Key recommendations of the IOF statement are:
• The estimated average vitamin D requirement of older adults to reach a serum 25OHD level of 75 nmol/l (30ng/ml) is 20 to 25 micrograms per day (800 to 1,000 IU per day).
• Intakes may need to increase to as much as 50 micrograms (2,000 IU) per day in individuals who are obese, have osteoporosis, limited sun exposure (e.g. housebound or institutionalised), or have malabsorption.
• For high risk individuals it is recommended to measure serum 25OHD levels and treat if deficient.
The dangers of a single annual dose
The statement coincides with the findings of study in the high-profile Journal of the American Medical Association (JAMA) that concluded that a once-a-year high dose of vitamin D may increase an elderly woman’s rate of falls and fractures compared to women who received placebo.
The trial randomly assigned 2,256 community-dwelling women over the age of 70 to receive either placebo or an annual oral dose of 500,000 IU of vitamin D3 (cholocalciferol) for between 3 to 5 years.
Australian researchers found that women in the vitamin D group experienced 15 per cent more falls than women in the placebo group. Furthermore, women in the vitamin D group had 26 per cent more fractures and a 31 per cent higher incidence of falls than women in the placebo group.
“This is the first study to demonstrate increased risk of falls associated with any vitamin D intervention and the second study to demonstrate an increased fracture risk associated with annual high-dose vitamin D therapy in elderly women,” wrote the researchers.
“Thus, it is reasonable to speculate that high serum levels of vitamin D or metabolites resulting from the large annual dose, subsequent decrease in the levels, or both might be causal. Furthermore, because the levels of 25-hydroxycholecalciferol demonstrated in this study could occur with other recommended dosing regimens, the outcome of this study suggests that safety of high-dose vitamin D supplementation warrants further study,” concluded the researchers.
In an accompanying editorial in JAMA, Dawson-Hughes and Susan Harris said the study supports the importance of continuing to improve understanding of basic vitamin D physiology, particularly as it relates to the increased variety of supplement forms that have become available by prescription and over-the-counter.
“In the meantime, it is important to reiterate that although vitamin D insufficiency is widespread, it can be safely corrected with a variety of existing supplement types and regimens and it should continue to be identified and treated in clinical practice,” added Dawson-Hughes and Susan Harris.
Published online ahead of print, doi: 10.1007/s00198-010-1285-3
“IOF position statement: vitamin D recommendations for older adults”
Authors: B. Dawson-Hughes, A. Mithal, J.-P. Bonjour, S. Boonen, P. Burckhardt, G. E.-H. Fuleihan, R. G. Josse, P. Lips, J. Morales-Torres, N. Yoshimura
2010, Volume 303, Number 18, Pages 1815-1822
“Annual High-Dose Oral Vitamin D and Falls and Fractures in Older Women: A Randomized Controlled Trial”
Authors: K.M. Sanders, A.L. Stuart, E.J. Williamson, J.A. Simpson, M.A. Kotowicz, D.Young, G.C. Nicholson
2010, Volume 303, Number 18, Pages 1861-1862
“High-Dose Vitamin D Supplementation - Too Much of a Good Thing?”
Authors: B. Dawson-Hughes, S.S. Harris