And people over 50 should be taking supplements up to 2,000 IU – the current ‘tolerable upper intake level’ – add the updated guidelines published in the Canadian Medical Association Journal.
Current Canadian recommendations are over a decade old and were not based on properly conducted dose-finding studies, says the journal.
“A daily supplement of 25 mg (800 IU) should now be regarded as a minimum dose for adults with osteoporosis,” states co-author Dr David Hanley from the University of Calgary Health Sciences Centre.
“Canadians can safely take daily vitamin D supplements up to the current definition of tolerable upper intake level (50 micrograms [2000 IU], but doses above that require medical supervision.”
The guidelines echo similar calls for the population to boost intakes of vitamin D. Typical recommended daily intakes (RDIs) lie between 200 and 600 international units (IU) per day while more and more science shows the above benefits can be better achieved with levels closer to 2000IU per day without safety concerns.
Some go much higher. One European study found daily doses between 2,000-3,000 IUs could reduce EU health care expenditures by €187bn ($250bn) each year.
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.
The IOM may also revise upper safe levels (USLs) with some saying 10,000 IU per day reflects the scientific literature – this would be a great boon to supplement manufacturers seeking to meet demand for high-dose products.
What is D?
Vitamin D refers to two biologically inactive precursors - D3, also known as cholecalciferol, and D2, also known as ergocalciferol. The former, produced in the skin on exposure to UVB radiation (290 to 320 nm), is said to be more bioactive.
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.
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
And the science supports maintaining adequate levels, with vitamin D deficiency in adults 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.