Where's the sunshine?
Autumn brings beautiful colours and crisp weather. But the season also brings fewer daylight hours, and when the sun does shine, it's at a lower angle. For Canadians, these changes can lead to vitamin D deficiency. Don't deprive yourself of this essential vitamin. Just be sure you're getting the right dose for you.

Vitamin D can do a lot
Vitamin D is crucial. "It has been well established that vitamin D is involved in [building] bone structure," says Dr. John Bosomworth, a retired family physician in Penticton, B.C., and author of a vitamin D research review. But, he says, more recent thinking links vitamin D to the immune system, inflammatory responses, blood supply and cell turnover. "Every tissue in the body has a vitamin D receptor," he says. "It would be no surprise if we found [the vitamin has] an influence on all these tissues."

Vitamin D may also play a part in protecting people from high blood pressure, certain types of cancer, chronic pain, respiratory infections and cardiovascular disease. As a topical agent, it's been found to treat psoriasis. And it may stall the progression of multiple sclerosis and ALS (commonly known as Lou Gehrig's disease). Much of this research, while promising, has been done on a small scale and needs more study.

Three ways to get your D
1. Sunshine
While your body can't produce vitamin D on its own, it can manufacture the vitamin when your skin is exposed to ultraviolet B light. But the UV index needs to be three or above. And for more than half the year, because of the angle of the sun in the Great White North, Canadians simply can't get proper exposure for the process to work. In the summer, you'd need to expose your skin, without sunscreen, for at least 10 minutes a day to get your D. But the strong summer sunshine comes with hazards too, including the risk of melanoma and other types of skin cancer, as well as premature skin aging.

2. Diet
Fatty fish and egg yolks naturally contain vitamin D, but in relatively small amounts. "Your fish intake would have to be a lot: a pound a day," says Dr. Reinhold Vieth, a professor of laboratory medicine and pathobiology, and nutritional sciences at the University of Toronto. The same limitation applies to vitamin-fortified foods such as milk, soy milk, and some orange juices and cereals. They help, but you'd need to drink six cups a day to get just 600 IU of vitamin D. Overall, though, dietary D options are limited, and the small amount these foods contain means it's nearly impossible to meet your needs through diet alone.

3. Supplements
Experts agree that the most reliable way get enough D is from vitamin supplements. They're inexpensive, don't require a prescription, and come in many forms and dosages, from 400 to 1,000 IU.

How much and what kind?
Convinced you need vitamin D but still have questions about how to take it? We've found answers to five questions that may help you make up your mind.

1. How much do I need?
That's a loaded question. For one thing, everyone's requirements are a little different (see One Size Does Not Fit All, below). But it also depends on who you talk to. Because evidence on vitamin D's effects is still emerging, the recommended daily intake remains a lively debate in Canada and elsewhere. Health Canada recommends 400 IU a day for babies, 600 IU for children and adults, and 800 IU for seniors over 70. Guidelines issued by the Washington-based Institute of Medicine are similar. Other researchers say these numbers are far too low. "Outdoor workers acquire the equivalent of 3,000 to 4,000 IU a day from summer sunshine," says Vieth. Osteoporosis Canada recommends up to 1,000 IU for healthy adults, and up to 2,000 IU for those in high-risk groups. A position paper from the Canadian Paediatric Society suggests 2,000 IU should be considered as a recommendation for pregnant women – and up to 4,000 IU for other adults.

2. Is it possible to take too much?
Anything can become poisonous when taken in a high enough dose. But researchers believe you would have to take more than 10,000 IU of vitamin D a day before approaching toxic levels. What's known for sure is that numerous clinical trials have administered 4,000 IU a day without causing any risk, so that's considered by Health Canada to be the tolerable upper limit for people age nine and over.

3. Should I take fewer supplements in the summer?
From April to September, the sun is at an angle in Canada that enables your skin to manufacture vitamin D. But that doesn't mean you should completely drop your supplements for the summer; quitting cold turkey can be hard on the body. It's OK to cut back, but if you take supplements steadily through the year, your levels are less likely to spike and fall with the seasons. Besides, if you're using sun protection such as sunscreen or are staying in the shade – both of which are strongly recommended by the Canadian Dermatology Association, and for good reason – you don't want to rely on sunshine for your vitamin D.

4. What kind of supplement should I buy?
With so many formulas on the market, it's tricky to pick one. Some experts say we're better at absorbing D3 than D2, while others say it makes little difference. (Most supplements sold in Canada are D3.) There's also debate about whether vitamin D is better absorbed in drop or gel form than in powder or tablet. "Take whatever form you will be most likely to stick with in the long run," says Vieth. (Honestly though, can compliance really be an issue for something that comes in chewable chocolate form?)

5. What happens if I skip a day?
Don't stress about it; you can just take more the next time. "Often one of the problems with taking supplements is adherence. We forget all the time," says Vieth. "If you forget a day – or two or three or four – you can catch up with vitamin D. It's forgiving."

One size does not fit all
When it comes to figuring out your vitamin D needs, there's no magic formula. Your ideal dose depends on a variety of conditions.

Obesity: Canadians who are overweight or obese need more vitamin D because of their body mass. This is similar to the way drug doses are adjusted to suit body size. Plus, larger people have a lower surface-to-volume ratio, so they're less likely to get the vitamin D they need through sun exposure.

Skin colour: People with dark skin are more likely to be deficient in vitamin D. That's because their skin pigments naturally block sun better.

Old age: It's long been believed that aging skin doesn't manufacture vitamin D as well. While new evidence disputes that theory, older people do tend to need more supplementation to keep their vitamin D levels up.

Young age: Exclusively breast-fed babies don't have a vitamin D source apart from the tiny amount in their mothers' milk. Liquid supplements sold especially for newborns can be given daily with an eyedropper. Children, of course, are building bone, and since vitamin D helps with calcium absorption, it's critical for them to get enough while their skeletons are still growing. What's more, adolescent girls who have a higher intake of vitamin D may have a lower risk of breast cancer in adulthood.

Motherhood: Pregnant women with low vitamin D levels have a higher risk of gestational diabetes. It's also possible they have an increased chance of developing preeclampsia.

Health conditions: Diseases that lead to fat malabsorption, such as cystic fibrosis, lactose intolerance, chronic liver disease or inflammatory bowel disease, can make it harder for the body to digest vitamin D. People with these conditions will need a higher daily dose of D.

The bottom line? It's better to be safe than sorry. "If you're somebody who is black, obese, lactose intolerant, getting older – it just piles one risk on top of the other. In my opinion, you have to think about going for a higher dose," says Bosomworth. "Like anything else in medicine, the decision to treat is all about determining risk."

Should I Get tested?
Is it worth it to have your vitamin D blood levels measured? Provincial health ministries say it's not necessary for the general population. Dr. John Bosomworth, author of a vitamin D research review, agrees. "It's an expensive test, and I'm not sure what we're measuring is necessarily reflecting what's going on with your health. We've done that with LDL cholesterol for years, and we're starting to understand that measuring your LDL cholesterol isn't the whole story." He believes it's more important to decide your vitamin D intake based on individual risk factors. There is little chance of overdosing.

Can I believe the bottle?
What if what's on the label doesn't match what's in the bottle? Dr. Erin LeBlanc, an endocrinologist at Kaiser Permanente Center for Health Research in Portland, Ore., discovered a disparity between the two in a recent study. Her team tested store-bought supplements in the U.S. and found that some pills contained up to 146 percent of the vitamin D dose listed on the label, while others had as little as nine percent. "People are paying for these vitamins with their own money," says LeBlanc. "They expect to get the amount on the bottle, and that's not always the case."

Gary Leong, vice-president of scientific and technical affairs at Jamieson Laboratories, believes the problem exists to some degree in Canadian products too. "There's a great amount of science and technical expertise involved in mixing powders together properly and uniformly," he says. And although Health Canada regulates the manufacture of natural health products sold here, Leong says it's up to the companies themselves to do internal product checks. "Licensing is granted based on self-attestation. In other words, it's all based on the honour system."

By all accounts, there's not a lot of risk involved in taking a supplement that contains more vitamin D than you think. "The main concern is if someone is getting [a supplement with a] low potency," says LeBlanc.

That's especially a problem if you're vitamin D deficient to begin with. When you're shopping, ensure that there is a Natural Product Number on the label. While that's no guarantee that the product is as strong as it's purported to be, it does mean Health Canada has at least reviewed and approved the potency information supplied by the manufacturer – unlike supplements without the number on their labels.

We've got lots more information about vitamins, including 10 foods that are vitamin-rich.

This content is vetted by medical experts

This story was originally titled "When the Sun Don't Shine" in the October 2013 issue. Subscribe to Canadian Living today and never miss an issue!