Vitamin D, aka the Sunshine vitamin, is actually considered a hormone. Although it is well known for its positive effect on bone health by helping the intestine absorb calcium and promoting bone mineralization, it has many other roles in the body. It enhances the secretion and action of insulin, the hormone that regulates blood sugar. It plays a part in the functioning of the neuromuscular system and cardiovascular system, it reduces inflammation, regulates cell growth, and sensitizes tissues to be more responsive to thyroid hormone. Vitamin D is also very involved in immune function. Receptors for vitamin D are expressed on the majority of immune cells.
Vitamin D is made in our skin after exposure to sunlight, specifically UVB light. It becomes active after enzymatic reactions in both the liver and kidney. A small amount of vitamin D can also be consumed in the diet from oily fish like salmon and sardines, cod liver oil, beef liver, and vitamin D fortified foods. However, it is hard to get enough vitamin D in the diet alone.
Vitamin D deficiency in kids results in a softening and deformity of the bones called rickets. Adults can get a similar softening of the bone called osteomalacia, which can be accompanied with bone pain, and muscle weakness and impairment. Vitamin D deficiency impairs immune function. There is an association between low vitamin D levels and several autoimmune diseases such as lupus, inflammatory bowel disease, rheumatoid arthritis, autoimmune thyroiditis, multiple sclerosis and type I diabetes. Poor vitamin D status has also been associated with increased susceptibility to viral and bacterial infections. Studies have shown that vitamin D supplementation can prevent acute respiratory infections, especially in very vitamin D deficient people. Observational studies have reported associations between poor vitamin D status and increased risk of developing colorectal and breast cancer. A study that was just released showed that high dose vitamin D given to patients hospitalized with COVID-19 significantly reduced ICU admissions and reduced the severity of the disease. Although this was a small study and needs to be carried out in larger trials, this is a pretty impressive result for our sunshine vitamin.
This brings us to the question - should I be taking vitamin D, and if so, at what dose? There is no one answer to this since everyone is different. There are certain factors that lead to vitamin D deficient or insufficient states that need to be taken into account. These include where you live, your age, the color of your skin, your weight, your sun exposure, genetic mutations in the vitamin D receptor, medications, as well as malabsorptive conditions of the gut. The only way to know how much to take is to check a blood level of vitamin D - 25(OH)D. There is some controversy on what the ideal level should be, but studies have shown that the sweet spot is somewhere between 40-60ng/mL. Levels in that range have been shown to decrease all-cause, cardiovascular, and cancer mortality in a recent study. Some feel higher levels are needed for certain conditions. There is a risk of toxicity if you do take too much - more is not always better.
Most people will not go wrong taking 2000IU of vitamin D3 daily, however many will need a larger dose. Getting some sunshine would be ideal and sneaking in some foods higher in vitamin D as well. Although there is just a small study showing a possible relationship between COVID-19 prevention and vitamin D, given its track record with other viral illnesses and its performance with hospitalized COVID patients, it is certainly in my regimen for keeping healthy in these crazy times.