It’s that time of year again when temperatures have dropped to their lowest, and it is likely your vitamin D levels have, too.

When the sun’s rays enter the Earth’s atmosphere at too much of an angle as happens during the winter season, UVB rays are blocked off, and your skin can’t produce vitamin D without them. Moreover, because you’re more likely to wear multiple layers of clothing and stay indoors when it’s cold outside, you reduce your exposure to sunlight even further.

The difficulty of getting enough vitamin D from food sources, such as fatty fish and dairy products, also contributes to low vitamin D.

Taking a supplemental form is an effective and safe way to get the vitamin D your body needs, but the type and amount of vitamin D you take matters. In fact, you may need a lot more than you’re getting, according to a recent landmark study in which Canadian scientists analyzed 108 separate, individual studies to create a meta-analysis.

The researchers concluded that subjects needed at least 3,000 IU of vitamin D per day to achieve and maintain adequate blood levels for optimal health. If overweight or obese, subjects required vitamin D at 5,000-7,000 IU per day.

Ongoing Debate

The study’s findings stand in stark contrast to the current Recommended Dietary Allowance (RDA), which is only 600-800 IU per day. The RDA is assumed to be enough to help the majority of the population achieve adequate levels of vitamin D.

However, the scientists discovered that the dietary recommendations may have been miscalculated due to a statistical error. There is also a large variability in how people respond to vitamin D intake that could mean that the current RDA may leave some people deficient.

The RDA may also vary across different body weights. For example, recent studies have found that obese individuals may need 2-3 times more vitamin D than people of a normal weight.

The type of vitamin D used to fortify foods could also be at issue when determining correct doses, since vitamin D2 (ergocalciferol) appears to be less effective compared to vitamin D3 (cholecalciferol) for raising levels of circulating vitamin D.

New Findings on Vitamin D Doses

The University of Alberta researchers sought out studies reporting dose-response relationships between vitamin D supplementation and active circulating concentrations. They also compared these with recordings from a nonprofit preventive health program in Canada.

The scientists concluded that the large variability in active circulating vitamin D “makes the RDA for vitamin D neither desirable nor feasible.” They then proposed for recommendations to be in a format that helps to optimize intake based on a combination of lower- and upper-circulating targets.

They recommended that optimal doses be body-weight specific. Based on their findings, a dose for normal weight individuals may need to be at least 3,000 IU per day, where as overweight and obese individuals may need to supplement with at least 5,000 IU per day.

The potential consequences of a low vitamin D status aren’t to be taken lightly either – a compromised immune system, premature cellular aging, compromised cardiovascular fitness, and even lessening of muscular endurance.


Veugelers PJ, Pham TM & Ekwaru JP. Optimal Vitamin D Supplementation Doses that Minimize the Risk for Both Low and High Serum 25-Hydroxyvitamin D Concentrations in the General Population. Nutrients. 2015 Dec 4; 7(12):10189-208.