Vitamin D

Updated: Feb 19

Vitamin D is a fat-soluble nutrient. It is one of the 24 micronutrients critical for human survival. The sun is the major natural source of the nutrient, but vitamin D is also found naturally in fish and eggs. It is also added to dairy products.


Supplemental vitamin D is associated with a wide range of benefits, including increased cognition, immune health, bone health and well-being. Supplementation can also reduce the risks of cancer, heart disease, diabetes and multiple sclerosis. People deficient in vitamin D may also experience increased testosterone levels after supplementation.


People deficient in vitamin D may also experience increased testosterone levels after supplementation.

The body produces vitamin D from cholesterol, provided there is an adequate amount of UV light from sun exposure. There is only a sufficient amount of UV light coming from the sun when the UV index is 3 or higher, which only occurs year-round near the equator, between the 37th parallels.


Most people are not deficient in vitamin D, but they do not have an optimal level of vitamin D either. Due to the many health benefits of vitamin D, supplementation is encouraged if optimal levels are not present in the body.


The Human Effect Matrix from examin.com summarises human studies to tell you what effects Vitamin D has on your body, how much evidence there is, and how strong these effects are.


Risk Of Falls: The risk of falls in the elderly (and subsequently, rate of bone fractures) appears to be significantly reduced with Vitamin D supplementation at 700 IU or greater, with most research in the 700-1000 IU range. Lower doses do not appear effective, and a greater protective effect appears to exist alongside calcium supplementation (and possibly Vitamin K supplementation)


Parathyroid Hormone: Vitamin D supplementation is the reference drug for reductions in parathyroid hormone due to directly negatively regulating its secretion.


Colorectal cancer risk: The association between serum Vitamin D at 37ng/mL and colorectal cancer is is approximately a halving of risk according to one meta-analysis, which is a notable risk reduction.


COVID-19 Severity: There is some evidence that vitamin D may improve inflammation and clinical symptoms in COVID-19 patients, but this may not hold true with all dosing regimens. So far, a few studies have shown that high dosages for 8–14 days may work, but a single high dose isn't likely to have the same benefit.


Functionality in the elderly: An improvement in muscular and neural functionality in the elderly is thought to underlie the reductions of fall risk and reduced bone fracture rate seen in elderly cohorts.


How to Take


The recommended daily allowance for Vitamin D is currently set at 400-800IU/day, but this is too low for adults. The Upper Tolerable Intake Level in the United States and Canada is 4,000IU/day. Research suggests that the true Upper Tolerable Intake Level is 10,000IU/day.


For moderate supplementation, a 1,000-2,000IU dose of vitamin D3 is sufficient to meet the needs of most of the population. This is the lowest effective dose range. Higher doses, based on body weight, are in the range of 20-80IU/kg daily.


Vitamin D3 supplementation (cholecalciferol) is recommended over D2 supplementation (ergocalciferol), since D3 is used more effectively in the body.


Vitamin D should be taken daily, with meals or a source of fat, like fish oil.


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