With winter and short days with little sunlight upon us, the supplement industry is busy telling us we need to supplement vitamin D or run the risk of dire consequences. But what does vitamin D do and how much of it do you really need?
What Is Vitamin D?
Vitamin D belongs to the family of fat-soluble vitamins and plays its biggest role in the human metabolism by keeping a check on how much calcium and phosphorus is in your blood and how much especially of the former is absorbed in the gut. As calcium helps developing and maintaining strong bones, vitamin D therefore is often used together with calcium to increase bone density and to lighten fractures.
Lately vitamin D has also been connected to helping against hypertension (high blood pressure), osteoporosis (brittling of the bones), cancer, and various other diseases, but the jury is still out on if it really has an effect on these and how big it may be.
There are a number of food sources containing vitamin D in higher amounts (eg. beef liver, whole eggs, fish), but it can also be formed by simply exposing your skin to the sun, which is where we usually get the highest amounts from.
The Sunshine Vitamin
Which leads us to the hook supplement companies aim for to sell us vitamin D supplements with. In line with the old school of supplement marketing, vitamin D sellers grasp any slight evidence for vitamin D doing anything to something (see above) and claim it’s a reason to watch out for how much vitamin D we are getting. Then we are breathlessly told how dire the risk of us running into vitamin D deficiency is, especially during winter. To make sure we get the hint, they finally don’t fail to mention that those of us with office jobs supposedly don’t even get enough of vitamin D during summer. Because we are indoors most of the time and vitamin D can’t be synthesized from sunshine that hits your skin through glass (which actually is true).
All this of course contrary to our ancestors, who supposedly were more “connected to nature” and “sensed” how important it is to toil away in the great outdoors. It is, I suppose, food supplement marketing 101 to mention the wisdom of our forefathers at some point to sell stuff , despite our ancestors being people who on average only had a life expectancy half as long as what we enjoy today and mostly thought that what couldn’t be cured by bloodletting and emetics was uncurable.
How Much And Where From?
The truth about vitamin D is much more complicated. Half an hour exposure to sunlight during the summer, just showing the world your bare arms and face, forms about 10,000 IU (“international units”) of vitamin D, or about 250 mcg (microgram). Which is an awful lot when we read that according to the Office of Dietary Supplements (ODS), the recommended daily allowance (RDA) for vitamin D for adults is just 600 IU (15 mcg).
The problem now is that how much we get from the bright, big ball in the sky can vary by huge amounts. On cloudy days those 10,000 IU normally gotten within thirty minutes are about halved. Another 60% are lost if you live in a city full of smog or have a darker complexion. And if you apply a sun screen with a protection factor higher than 7 or if you are black, you will synthesize very little vitamin D. Not to mention that too much exposure to sunlight plays a big role in skin cancer and risking that to get enough vitamin D isn’t that swell an idea either.
On the other hand, in the US, and again according to the ODS, males consume to 204 to 288 IU per day from their nutrition, females 144 to 276 IU, therefore getting about half their RDA that way. This is not due to a so far secret love Americans have for beef liver, but to many foods in the US being fortified with vitamin D. In Europe vitamin D fortification is almost unheard of and deficiencies therefore potentially more likely.
The Big Ole Recommendation
As stated above, vitamin D is a fat-soluble vitamin and if you read my article on the different vitamins then you know that overdosing those generally is not a good idea. For vitamin D the maximum amount is still hotly debated, even though the ODS currently states the maximum daily amount you should have as 4,000 IU. That is a bit absurd, if just half an hour of sunlight generates 10,000 IU. If already 4,000 qualify as maximum, then at least in the southern US and southern Europe, where people during the summer spend way more time in direct sunlight, we should yearly see hundreds of cases of acute vitamin D overdoses.
The numbers at which the symptoms of vitamin D deficiency occur are established a bit better, and we can therefore use those as a guide. If you are an adult and live in the northern US or Canada, a vitamin D supplement containing 1,000 IU every second or third day during the winter should about cover your needs. In northern Europe, where food usually isn’t fortified, the same amount every day or every second during winter should do the same.
Yes, I did recommend usage of a vitamin supplement, but only with caution and pertaining to specific circumstances under which it may prove useful. Do keep in mind that this indeed is just a recommendation and various factors play a role in how much vitamin D is needed and safe for you to supplement. If you are in doubt and want to find out for sure how much you need, you should get your vitamin D level checked by your doctor.