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.
A little sunlight can go a long way
The amount of sun exposure needed to produce enough vitamin D depends on:
- age
- diet
- skin colour
- where you live
- how strong the sun is
A few minutes a day of unprotected sun exposure is usually all that is needed for some people to get enough vitamin D. You don’t need a tan to get benefits from the sun. Even with the benefits of vitamin D, we recommend that you still practice SunSense.
Vitamin D supplements
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 exclusively 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.
Learn more about vitamin D from Health Canada
Who’s 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 1000 IU every day, all year round.
Can you have too much of a good thing?
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.
Getting the right amount of vitamin D
For most adults, taking a supplement of 1000 IU (international units) a day won’t be a problem. But there is most likely an optimal range of vitamin D – having either too little or too much can cause health problems.
Side effects of too much Vitamin D
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 also shows that there may be other health conditions made worse from too much vitamin D. Some studies have also 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.
Health conditions and vitamin D
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
- sarcoidosis and other granulomatous diseases
- 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.
What research shows
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 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. In their 2008 report, they concluded that:
- there is a relationship between low vitamin D and colorectal cancer
- there is limited evidence for breast cancer
- there is no evidence for prostate cancer
Read the IARC report.
The Institute of Medicine (IOM) is an organization that reviews research and provides advice to governments in Canada and the US. For example, they provide recommendations on specific nutrients like vitamin D and how much to take. Because of all of this new research, the IOM updated their recommendations in 2011, 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
Read more about the IOM report.
Why is more research 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 vitamin D, we still can’t say for sure that the vitamin D is the cause.
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. For example, there was a large randomized controlled trial called the SELECT trial that tested the effect of taking vitamin E and selenium supplements. In observational studies, these supplements were shown to decrease the risk of prostate cancer. The RCT found the opposite – an increase in the risk for prostate cancer with vitamin E and an increase in diabetes with selenium. The trial was stopped early when researchers found that these supplements were not reducing cancer risk and could cause harm.
At least 1 vitamin D RCT is underway in the US, though it will be a while before we know the results. The VITAL study (Vitamin D and Omega-2 trial) will include 20,000 men and women and will study whether taking a vitamin D supplement or fish oil supplements can reduce the risk of cancer or cardiovascular disease.