With days getting shorter and temperatures getting colder November is the month to think about vitamin D. That’s because our bodies’ process for manufacturing the “sunshine vitamin” requires sunlight on our skin and with fewer hours of sun, medications less time outdoors and more surface area covered by clothing we’re at a time of year when we don’t have as much opportunity to meet our vitamin D needs.
While we’ve long understood this reality, research over the past decade has revealed three important new findings about vitamin D:
1) The proportion of North Americans with low levels of vitamin D has risen, possibly due to efforts to reduce sun exposure to help lower the risk of skin cancer
2) Insufficient vitamin D doesn’t just cause “rickets” (softening of bones), it also may increase our risk for several other diseases, including cancer (particularly colon cancer), heart disease, stroke, dementia, depression, diabetes and multiple sclerosis
3) We can take larger doses of vitamin D supplements than we previously thought before causing vitamin D toxicity
As a result, we have seen lots of press about the importance of getting enough vitamin D, the need to get tested to determine whether or not we might be deficient and the desirability of supplements.
However, the latest research has already cast doubt on some of these findings and recommendations. And that’s made it more confusing to know the best course of action for the average patient. With that in mind, let’s look at best advice on vitamin D as we head into winter.
To begin, we now recommend against routine testing for vitamin D (see the Choosing Wisely website). That’s because we don’t have good research that shows how vitamin D levels correlate with our disease risk, which means that test results can’t guide our decisions.
With respect to that correlation, we haven’t been able to show that having smaller amounts of vitamin D in our bodies actually causes the significant events and illnesses listed above. Instead, it may be the other way around – the diseases lead to lower vitamin D – or that an unidentified third factor leads to both disease and low vitamin D (for a review of association vs causation, see the post Did my annual checkup cause my car accident?)
That uncertainty would be unimportant if we could instead show that consuming more vitamin D, either through food or supplements, would reduce our risk of these diseases. However, an analysis of studies done through 2013 did not show meaningful reduction in likelihood for any important disease from taking vitamin D.
Which is where the third of the recent research findings – what levels of vitamin D intake are safe – comes in.
As summarized in this Mayo Clinic report from earlier this year, warnings about vitamin D toxicity that originated in the 1950s led to longstanding caution when creating intake recommendations. However, 2010 guidelines for adults and children aged 9 and older increased the recommended daily amount to 600 IU (international units) and set 4,000 IU as the daily maximum.
Those amounts create a much wider range of safe consumption, making it easier to assure that we achieve the minimum recommend amount because we don’t need to worry about taking too much.
So how should we get our vitamin D?
As noted at the beginning of this post, exposure to the sun, specifically its ultraviolet B waves (UVB), quickly leads to vitamin D production in our bodies. However, the amount of sun exposure that we require depends on sun intensity, the amount of uncovered skin and the season (there is little UVB in the winter throughout much of North America). We also have to contend with the fact that the sunscreen that we use to block UVB and prevent skin cancer leads to lower production of vitamin D.
That means that we have to partly rely on consuming vitamin D in our diets. Though fish and egg yolks are the foods that have naturally high amounts of vitamin D, nearly all milk in the US and Canada is fortified with vitamin D. As a result, most of us can meet our vitamin D needs with what we eat and drink.
However, some of us don’t meet those needs. And since our body won’t overproduce vitamin D from sun exposure (a nice safety feature) and because it’s exceptionally difficult to reach maximum daily vitamin D levels through food intake – it takes about 8 quarts/litres of milk, 100 eggs or 8 cans of salmon – there is essentially no risk for adults and children aged 9 and older to take the standard supplement dose of 1,000 IU daily (children aged 1-8 can take 600 IU and infants 400 IU).
While the likelihood of us needing a vitamin D supplement is greater in the winter, I recommend that my patients take it year round. That’s because my experience is that people have a hard time remembering to re-start a treatment that they take for only part of the year and also because I’m a strong advocate for using sunscreen at all times.
The bottom line: if you’re older than age 8 and don’t already take 1,000 IU of vitamin D, now is a particularly good time to start. And given that there’s no downside but some suggestion of significant new benefits for maintaining adequate vitamin D in our system, it makes sense to take it continuously.