Osteoporosis Canada (OC) is aware that the September 24 news broadcast on CBC’s The National, regarding a recently published study of vitamin D and calcium supplementation, may cause some confusion as to the recommended amount of vitamin D one needs per day. OC recommends 400-1,000 IU daily for those under 50 at low risk of fracture, 800-2,000 IU daily for those 50+ or who have osteoporosis, have fractured, or are at high risk of fracture. These recommendations are safe and well below Health Canada’s upper limit for vitamin D intake.
Here is part of Dr. David Hanley’s response to the CBC:
“… The CBC’s National closed with the suggestion that people should consult their physician before taking more than 800 IU/day. This will cause anxiety among many Canadians, and will probably encourage many unnecessary patient interactions with healthcare providers. That recommendation has no justification in clinical practice. Health Canada’s Tolerable Upper Intake Level (TUL) for vitamin D is 4,000 IU/day. By definition, a TUL of 4,000 IU/day means this is the highest level of daily vitamin intake that is likely to pose no risk of adverse health effects to almost all individuals in the general population. In practical terms, this means that a patient should not take a supplement of 4,000 IU/day or higher without medical consultation or supervision. The Osteoporosis Canada recommendations are well below the TUL. The CBC reported Health Canada and the Institute of Medicine recommendations correctly at 600 or 800 IU/day. But the Osteoporosis Canada recommendations are safe, and are more likely to consistently provide bone benefit/protection for osteoporosis patients or people at risk for vitamin D deficiency than the Health Canada recommendations for the general population.” Regarding the particular study cited in the news item, Dr. Hanley noted that the study did not look at the standard outcomes of a study of a bone treatment intervention – i.e. fractures or bone density. The paper only looked at short term effects of high dose vitamin D and calcium supplementation on blood levels of biochemical markers of bone turnover. Bone turnover markers are surrogate outcomes that need to be interpreted in the context of other observations like fractures or bone density. The study showed that if a patient starts out with an adequate level of vitamin D, increased calcium intake, but not increased vitamin D intake, was able to suppress bone turnover. Suppression of bone turnover markers is predictive of bone benefits with some osteoporosis treatments like bisphosphonates, but bone turnover markers are increased by bone-building treatments like teriparatide. Vitamin D has complex effects on bone, and increases some markers of bone turnover, so it is perhaps not surprising that it might not have the same effect on bone turnover as calcium supplementation. Dr. Hanley concluded, “It is an oversimplification to suggest that this study shows that vitamin D does nothing for bone strength if patients start out with what the authors called adequate vitamin D levels. To the best of my knowledge, no one has done a long-term study to assess the comparative effects of increasing daily doses of vitamin D (up to the TUL) on bone quantity and quality.”
Dr. David Hanley is a Professor in the Departments of Medicine, Community Health Sciences and Oncology, Division of Endocrinology and Metabolism at the University of Calgary.