High-dose Vitamin D Supplementation: Is it safe and effective?

By Dr. Iva Lloyd, ND

There has been a lot in the media over the last couple of years encouraging people to take high doses of vitamin D. The potential benefits of supplementation include:

• fewer falls and fractures
• increased bone density
• prevention of influenza virus
• prevention or reduction in asthma attacks
• increased insulin sensitivity
• decreased blood pressure
• and the prevention of some cancers and autoimmune disease

Not that long ago the recommended dosage for vitamin D supplementation was 400 IU / day.  Currently it is not unusual for individuals to be dosing at 10 to 20 times that amount. Lately it has been questioned whether or not the benefits of vitamin supplementation are still achieved at high dosages. The concerns include:

• Serum 25 hydroxyvitamin D (the standard blood test for vitamin D status) may not be a reliable indicator as it's half-life is 3 weeks. Also, 25 hydroxyvitamin D is only one of more than 50 vitamin D metabolites in blood and it is questionable as to the validity of using it as the primary indicator.
• The safety and efficacy of vitamin D supplementation cannot be inferred from data regarding the safety and efficacy of sunlight exposure. Many of the promoted benefits of vitamin D supplementation are actually from studies looking at sunlight exposure itself.
• Vitamin D is a fat-soluble nutrient and hence it can accumulate within the body and cause other concerns. For more information: http://www.ndhealthfacts.org/wiki/Vitamin_D
• Most of the studies on vitamin D supplementation are less than 20 weeks long hence the long-term safety of dosages greater than 2,000 IU/day is questionable.
• Vitamin D levels decline in response to inflammation. Therefore blood work that indicates low levels of vitamin D may be more indicative of inflammation level versus vitamin D status.
• There are some studies that indicate that vitamin D supplementation may exacerbate atherosclerosis.
• Studies suggest that moderate dosages of vitamin D may be protective against cancer; whereas high doses were not and may actually increase the risk.
• Bone density measurements were better with low-to-moderate dosages of vitamin D.

There are some conditions, such as Celiac disease, Crohn's, multiple sclerosis and some cancers where dosing high with vitamin D may be advantageous.  The new research indicates that 800 to 1200 IUs / day is generally effective for most people. Ideally, the best way to ensure adequate vitamin D status is to enjoy 5-15 minutes of sunlight exposure 2 to 3 times a week between 10 a.m. and 3 p.m.  For the majority of people living in Canada vitamin D supplementation is advisable between October and March when the amount of sunlight is limited.

If you have any questions about the optimal amount of vitamin D supplementation for yourself, talk to your naturopathic doctor.

Reference:
Gaby, Alan 2011 Controveries in Nutrition. Presented at the Ontario Association of Naturopathic Doctors annual Conference.