Vitamin D
Vitamin D is a very important vitamin which unfortunately is deficient in many people It is one of four fat soluble vitamins (the others are vitamins A, E and K) and it acts as a hormone in the body. It plays a vital role in bone health and may have many other benefits outside of preventing osteoporosis. Some studies suggest that low vitamin D levels may increase your susceptibility to infectious diseases such as COVID-19.1 Vitamin D may also improve the bacteria in your gut (your microbiome) and help with inflammatory disorders and multiple sclerosis.2
Vitamin D is produced by the skin when exposed to sunlight. In general, people living north of the 37th parallel (San Fransico on up on the west coast, north of the state of Texas in the midwest and Richmond, Virginia on up on the east coast of North America) need vitamin D supplementation, especially in the winter months. In addition, two groups may need higher doses - those with darker skin and those with higher body mass indexes (BMIs).
During the shorter half of the year (October through March in the northern hemisphere), I advise most people to take 1,000 IUs a day and those with darker skin or higher BMIs to take 2,000 IUs a day. I recommend testing for vitamin D (which is not covered by OHIP) to receive more precise recommendations. With my weight loss patients, I will regularly test for vitamin D levels as often they need higher doses to maintain ideal levels of vitamin D.
Since vitamin D is a fat-soluble vitamin, it should ideally be taken with your biggest meal of the day which contains fat.3 At least one study has shown that it is 32% better absorbed after a meal containing fat than after a fat-free meal. 4 Alternatively, you can take vitamin D in a liquid form where it is already mixed with oil. In general vitamin D in liquid form is absorbed significantly better than in tablet form. However the drops can be quite a bit more expensive.
The safe upper limit of vitamin D supplementation is 4,000 IUs a day. Because it is fat-soluble, excess amounts can be stored in your body and cause toxicity. Symptoms of toxicity include abdominal pain, decreased appetite and kidney stones. Do not take more than 4,000 IUs a day unless you have been instructed to do so by your health care professional and are having your vitamin D level tested routinely.