Vitamin D is needed for healthy bones and muscles, especially in children and the elderly. There is growing evidence that vitamin D may reduce the risk of some types of cancer, particularly colorectal and breast cancers. Experts are now concerned that many people are not getting enough vitamin D.
You can get vitamin D from exposure to sunlight, in your diet (especially if you eat foods fortified with vitamin D) or by taking vitamin supplements.
How much vitamin D?
Due to our northern latitude and because the sun’s rays are weak in the fall and winter, we recommend that Canadian adults consider taking a vitamin D supplement. Talk to your doctor about taking 1000 international units (IU) a day during fall and winter months.
Babies who are only breast-fed might be at risk of vitamin D deficiency, which is why experts recommend they be given a vitamin D supplement of 400 IU a day. For more information on recommended vitamin D intakes for breast-fed babies and other age groups, go to Health Canada.
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If you are at higher risk
You’re probably not getting enough vitamin D if you:
- are over 50
- have dark skin
- don’t go outside very much
- wear clothing covering most of your skin
If you are in one of these groups, talk to your doctor about whether you should take a vitamin D supplement of 1000IU every day, all year round.
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Taking too much
We don’t recommend taking any more than these amounts because too much vitamin D can be harmful. Current evidence suggests that taking this amount will help reduce your risk of cancer but with the least chance of harm.
There is most likely an optimal range of vitamin D. Having either too little or too much can cause health problems. The most common side effect of having too much vitamin D is high calcium levels, called hypercalcemia. Some early symptoms of hypercalcemia include:
- nausea
- vomiting
- poor appetite
- weakness
Talk to your doctor if you are experiencing any of these symptoms.
More serious health problems can develop from chronic hypercalcemia such as kidney stones and deposits of calcium and phosphorus in organs and soft tissues. For most people, this happens only when taking very high levels of vitamin D supplements along with calcium supplements. This side effect is not seen from vitamin D that is naturally made in the skin.
Some early research shows that some health conditions may be made worse from too much vitamin D. Studies have found an increase in overall mortality and in chronic diseases such as cancer and heart disease from higher vitamin D levels. These effects were seen at vitamin D levels that are lower than those causing hypercalcemia, but still much higher than what Canadians typically have. More research is needed to better understand these early findings.
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Sensitivity to vitamin D
For most adults, taking a supplement of 1000 IU a day won’t be a problem. But there are some health conditions that can lead to a sensitivity to vitamin D. This is when normal levels of vitamin D can cause health problems such as hypercalcemia. You may be at risk for this condition if you have any of the following:
- primary hyperparathyroidism
- Hyperparathyroidism is a condition in which the parathyroid glands make too much parathyroid hormone.
- sarcoidosis and other granulomatous diseases
- Sarcoidosis is a disease that results from inflammation of tissues of the body. It can appear in almost any body organ, but it most often affects the lungs or lymph nodes. Granulomatous diseases include a wide variety of disorders that cause tumour-like masses called granulomas to form.
- non-Hodgkin lymphoma
Depending on your health history, your doctor may want to watch your vitamin D levels closely or even take other measurements such as calcium levels. Talk to your doctor about possible complications when taking vitamin D supplements.
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Vitamin D and cancer
Research from many observational studies over the last 20 years has shown a relationship between vitamin D and cancer risk. A number of studies have also been published looking at the relationship between vitamin D and other health conditions such as heart disease, diabetes and multiple sclerosis.
The International Agency for Research on Cancer (IARC) brought together a working group to review the evidence on vitamin D and cancer. The working group concluded that:
- There is a relationship between low vitamin D levels and colorectal cancer.
- There is limited evidence that there is a relationship between low vitamin D levels and breast cancer.
- There is no evidence that there is a relationship between vitamin D levels and prostate cancer.
The Institute of Medicine (IOM) is an organization that reviews research and provides advice to governments in Canada and the US. They provide recommendations on specific nutrients like vitamin D and how much to take. Because of new research, the IOM updated their recommendations on vitamin D, concluding that:
- Vitamin D plays an important role in bone health.
- There is not enough evidence to be certain that vitamin D plays a role in other health outcomes, including cancer.
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More research is needed
The current body of evidence around vitamin D and cancer consists of many observational studies and only a small number of small randomized controlled trials using supplements. The participants in most of these randomized controlled trials were given a supplement of calcium as well as vitamin D. While most of the research results are consistent in showing a relationship between cancer and low vitamin D levels, it’s too soon to say for sure that increasing vitamin D levels will reduce cancer risk.
A large randomized controlled trial (RCT) is needed to show that changing your vitamin D levels will change your cancer risk. This type of research study is considered the “gold standard” in research, but is very expensive and takes a long time to conduct. An RCT can confirm whether vitamin D plays a role in preventing cancer. It can also give researchers a better understanding of:
- the levels of vitamin D in the body needed to help prevent disease
- the amount of vitamin D needed for maximum benefit
- diseases, including specific types of cancer, that may benefit from optimal vitamin D levels
Research on other dietary supplements has shown that observational studies are not enough to fully understand the effects of supplements.
At least one randomized control trial, the VITAL study (Vitamin D and Omega-2 trial), is underway to see if taking a vitamin D supplement reduces the risk of cancer or heart disease. It will be a while before the results are known.
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