Vitamin D – A Hormone for All Seasons!

Vitamin D deficiency is a major public health problem worldwide in all age groups. Even countries with low latitude where it was generally assumed that UV light radiation was adequate enough to prevent D deficiency, and in countries where vitamin D fortification was implemented in foods.

More than 50% of Canadian children have vitamin D levels below the Canadian Paediatric Society recommendation. According to Statistics Canada, about 40% of Canadians were below the cut-off in winter, compared with 25% in the summer and 59% of those aged 20 to 39 had the lowest level of vitamin D.

People over the age of 50 have increased risk of vitamin D deficiency and the risk increases with age. As people age, they lose some of their ability to synthesize vitamin D from sunlight. D also needs to be activated in the kidney before being absorbed and this function also decreases with age. Finally older people who are homebound are less likely to get outdoors in the sun.

Vitamin D is a fat-soluble steroid hormone with numerous cellular functions. The body makes vitamin D in a chemical reaction that occurs when sunlight hits the skin; it is also found in some foods such as fatty fish (salmon, sardines, tuna, cod liver oil), egg yolks and shiitake mushrooms and supplemental forms.

Before vitamin D can be used by the body it needs to be converted from its inactive form to an active form in order to exert its biological functions. Many of these various conversions and transport throughout the body are actively dependent on the bioavailability of magnesium.

A recent study by Health Canada showed that more than 34% of Canadians have a magnesium intake below the estimated average requirement. Abnormal levels in either of these nutrients can lead to many mental and physical health disorders and magnesium deficiency is contributing to the increasing levels of vitamin D deficiency in the general population.

Some observational and preliminary studies suggest that vitamin D3 deficiency can result in obesity, diabetes, cardiovascular disease, depression, osteoporosis and certain cancers.

Other studies say there is not enough evidence. Absence of evidence does not mean evidence of absence.

Vitamin D also aids in the function of brain cells and deficiency has several consequences when it comes to brain health. There is a greater risk for cognitive impairment, dementias, depression and learning disorders.

Vitamin D is also very important for the immune system. Studies have shown that it can modulate both the innate and adaptive branches of the immune responses. The innate immune system provides a general defense against common pathogens (bacteria, virus, other microorganisms). The adaptive immune system targets specific threats and has precise responses against viruses or bacteria that the body has already come into contact with. The various components of the immune system work together to provide both types of protection. Vitamin D deficiency is associated with increased susceptibility to infection.

There are also debates around the recommended dosage for vitamin D and it varies greatly depending on what you read or who you talk to. Some reasons for this variable opinion may depend on the overall health of the individual, whether they are confirmed ‘deficient’ by lab tests, their diet, sun exposure, and their magnesium status.

August 2020 Health Canada Vitamin D Update

With the mounting interest from stakeholders, and given the increase in scientific evidence regarding supplemental vitamin D3, Health Canada’s Food Directorate undertook a safety assessment to determine whether sufficient safety information existed to support raising the maximum non-prescription vitamin D3 level up to 2,500 IU. Results showed that 2,500 IU would provide a safe maximum level of vitamin D in non-prescription supplements for children 9 years and older, adolescents and adults.

Health Canada

BC health care insurance no longer covers general vitamin D test even though it is one of the most important tests every person should have yearly. The test when requisitioned by your MD or ND is available for approximately $65.00. However, even without testing, supplementation of 2,000-4,000 IU provides adequate levels for most healthy people. The ‘at risk’ groups may require higher levels. 

Studies have shown that certain ‘at risk’ groups of people require higher levels of vitamin D.

Overweight and obese people required at least 7,000 IU to 8,000 IU daily to achieve adequate status.

In addition to these groups, other groups at risk for vitamin D deficiency include: breast fed infants, older adults, people with limited sun exposure, people with dark skin, people with fat malabsorption problems, and pregnant women.

It might be wise for most people to follow the Tolerable Upper Intake level in the above chart, especially during the winter months, and all year long for those who get little sun exposure, the elderly and those who wear protective sun clothing or sunscreen during summer months.

Risk of Toxicity

The National Academy of Medicine has stated vitamin D intake above 4,000 IU/day may cause toxic effects such as renal impairment, hypercalcemia or vascular calcification. The Mayo clinic set out to learn about the health of those taking high vitamin D levels. They found that toxic levels are actually very rare.

Remember it is very important to take vitamin D with a fatty meal, and remember the addition of magnesium for more efficient vitamin D absorption. In addition, it is very important that children receive adequate vitamin D supplementation.


Reddy P, Edwards LR. Magnesium Supplementation in Vitamin D Deficiency. Am J Ther. 2019 Jan/Feb;26(1):e124-e132.


Karen Jensen was in clinical practice for 25 years and although she is retired, she continues to write books and educate on the naturopathic approach to wellness. She is author or co-author of seven books, her most recent is Women’s Health Matters: The Influence of Gender on Disease.

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