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The Vitamin “D”ebate

April 6, 2010

Fondly known as the “sunshine vitamin,” vitamin D has been receiving a growing amount of attention lately – and with good reason!  Not only is this fat-soluble vitamin absolutely crucial in the prevention of rickets and osteomalacia (conditions of decreased bone mineral content in children and adults respectively), studies have shown it may play a role in alleviating psoriasis, osteoporosis, hypertension, autoimmune conditions, reducing heart attack risk as well as cancer prevention.

The Facts

The term “vitamin” represents any of the “vital amine” compounds which have been found as an absolute requirement for good health.  For vitamin D, its absolute requirement is to prevent rickets and osteomalacia, as described above.  The forms utilized by humans are ergocalciferol (Vitamin D2) which is produced by plants, and cholecalciferol (Vitamin D3) which is created from skin exposure to the UVB rays of sunlight, a process which converts precursors to the active form of vitamin D.  It can also be found in fortified foods including fish, eggs, fortified milk and cod liver oil.  Upon entering the body vitamin D plays crucial roles in calcium absorption into the muscles and bones as well as balancing calcium and phosphate levels in the blood.

How Much Vitamin D is Recommended?

This is where the debate arises.  The dietary reference intakes (DRI’s) recommended by Health Canada range from 200-600IU’s per day, with increased levels recommended for the elderly due to the increased risk of osteoporosis.  The established tolerable upper intake level is 2000IU across the board, due to the potential for vitamin D toxicity.

Dietary Reference Intakes for Vitamin D (IOM, 1997)

Age groups
Adequate Intake (AI)
(for men and women)
Tolerable Upper Intake Level (UL)
(for men and women; chronic exposure)
19-50 years 5 μg (200 IU) per day 50 μg (2000 IU) per day
51-70 years 10 μg (400 IU) per day
>70 years 15 μg (600 IU) per day

Questions have arisen, however, as to whether these levels alone are sufficient to meet the body’s physiological needs, especially in individuals who tend to receive less exposure to sunlight.  A survey recently conducted by Stats Canada found that two out of three Canadians has less than the recommended level of vitamin D shown to prevent chronic diseases, while one in ten has less than the recommended amount to maintain adequate bone health.  As albeit proud members of a somewhat sun-starved country, if we wish to be able to boast about our Canadian heritage into our 90’s we may need to increase our vitamin D intake beyond the DRI levels to increase our chances of doing so!

Precautions about Vitamin D

Although the health benefits of higher levels of vitamin D are numerous, this doesn’t necessarily imply “the more the merrier.”  Vitamin D is fat-soluble (along with vitamins A, E & K) implying that unlike many other vitamins, you can store extra vitamin D in your body’s fat cells.  As with most vitamins, there is a risk of developing toxic effects with too high of an intake which is why any vitamin D hype should be carefully heeded and followed up with appropriate measures.

One repletion study by Pepper (2009) gave 50,000IU of vitamin D2 per week for four weeks, followed by 50,000IU monthly for another five months.  This initial dose is over 3.5 times the established tolerable upper intake level.  As a secondary point, by the end of the study two thirds of the subjects still did not reach the 75nmol/L blood serum level that has been reported to achieve many of vitamin D’s cancer and heart disease prevention benefits.  In comparison, a study by Aloia (2008) gave subjects only 2000IU of vitamin D3 per day for 8 weeks and found that with this lower dose using the cholecalciferol form subjects were able to reach the recommended 75nmol/L serum vitamin D levels established as being preventative!

Toxic levels of vitamin D can cause hypercalcemia, a condition of increased calcium levels in the blood which may lead to bone loss, impaired kidney function and calcification of other organs in the body.  Early signs of hypercalcemia include nausea, vomiting and anorexia (loss of appetite).

What does all this information mean?

A number of things…

1. Too little vitamin D is a bad thing. Being Canadians our yearly sun exposure is too low to provide adequate vitamin D alone, and even by taking fortified foods this is a tough goal to reach.  Low levels (serum concentrations below 25nmol/L) can place a person at risk of various bone diseases and does not allow them to reap the preventative benefits of vitamin D on cancer, heart disease, and autoimmune conditions.  At a bare minimum, we need to take in 200-600IU’s of vitamin D on a daily basis.

2. Too much vitamin D is a bad thing. Despite recent trends to high-dose vitamin D supplementation for preventative means, this does not come without hazards.  High levels place a person at risk of developing hypercalcemia, kidney impairment and organ calcification.  Thus if a person chooses to do high-dose supplementation this absolutely must be accompanied by corresponding blood serum measures to assess appropriate vitamin D levels.

3. 2000 IU of vitamin D is a safe daily intake level. Although tolerable upper limits for this vitamin may change in the near future, regular daily intake of this level has not shown any side effects and is safe for the general population.

In the mean time don’t forget that there are many other health benefits from sun exposure and healthy eating habits.  Summer is just around the corner so I recommend we all get outside, enjoy the fresh air and instead of a burger perhaps throw a piece of vitamin D-enriched salmon on the grill!

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