Saturday, December 4, 2010

Vitamin D vs. Winter Weight Gain

A kind of nutritional skirmish broke out over vitamin D this week, when a scientific group raised its recommendations for vitamin D, and government authorities in the United States and Canada responded by warning people not to take too much.

People could get the wrong idea from the government statements. Vitamin D is relatively nontoxic compared to other vitamins. Healthy people in scientific studies had to take a week’s worth of vitamin D supplements every day to produce toxic effects, and even then, it took months of this kind of extreme excess before the first symptoms appeared.

I’ve never known anyone to take vitamin D pills one after another. Rather, the situation most people are in, particularly in the northern United States and Canada and particularly at this time of year, is a shortage of vitamin D. The average person needs more, not less. Trying to scare people away from taking vitamin D supplements (and even the dairy products that have vitamin D supplements added) is sending the wrong message.

The recent government statements on vitamin D are misleading in another way. They emphasize bone health, as if the main function of vitamin D was to hold your bones together. The truth is quite otherwise. Vitamin D is tied into thousands of processes in the body, from hormone levels to metabolism. Vitamin D protects against cancer and diabetes, though scientists are still trying to figure out how this works. In long-term studies, people who take vitamin D supplements die 7 percent less often than people who don’t. It’s not just about the bones.

Vitamin D is the one major nutrient that is directly related to the seasons, if you live in a place that has distinct seasons. In late spring and summer you can get all the vitamin D you need from sunshine, and you won’t need to eat any of it. If you are out in the sun with a small fraction of your skin uncovered for an average of several minutes a day, that’s probably enough. The skin synthesizes vitamin D easily in full sunlight. It is a different story in the winter when the sun is not so bright and people are not outside much. That’s why this is the time of year when people should be thinking about vitamin D. It is this situation that the vitamin D guidelines are intended for. The new guidelines recommend 600 IU of vitamin D per day for adults who don’t get any sun, or up to to 4,000 IU. Notice that the recommendation allows for a very wide range, and chances are, you can exceed the maximum by a factor of 10 without any problems as long as you don’t do so day after day. Besides, the maximum isn’t intended as a limit for a person who has a vitamin D deficiency, but as a guideline for people who are passive about their nutrition, to prevent an excess from building up. Still, the lower number, the reference value of 600 IU, is probably all you need.

You need to know about vitamin D if you are overweight and tend to gain weight in the winter. Urban folklore pins the blame for the added weight on holiday meals, but the scientific evidence points more to vitamin D. More recently, scientists have made a link between vitamin D and seasonal depression. It makes sense to me, if you have any kind of problem with winter, to look at vitamin D.

Vitamin D deficiency is surprisingly common. In the United States, nearly 60 percent of people who are tested for vitamin D are deficient. Of course, people with illnesses are more likely to be tested, but still, only about half of U.S. adults have enough vitamin D to be healthy according to medical guidelines. Obviously, if you are not out in the sun regularly and are not taking a vitamin D supplement, the odds that you are getting enough vitamin D are lower.

The simple answer to vitamin D, if you have the kind of deficiency most people seem to have in winter, is to buy the smallest vitamin D supplements you can find (the bottle will say “D3”) and take one per day — or actually, one every four days would probably be enough. Unlike other nutrients, trying to get vitamin D from food is not necessarily the right approach. Most of the vitamin D you find in food is in milk, and this is a supplement added to the milk (that’s why it’s called “vitamin D milk”). You get the same supplement in a vitamin D capsule, and without the health consequences that come with consuming dairy products.

Even better, as soon as weather permits it, get out in the sun for minutes at a time. Where I live in southern Pennsylvania, I only need a vitamin D supplement between November and March.

Vitamin D is fat-soluble, so it doesn’t so much matter how much you get in one day — it’s more a matter of how much you get over the course of a month. All vitamin D supplements contain more than the daily reference amount, so you may not need to take them every day. A 2,000 IU capsule has enough for 3.3 days, so if you want to be conservative about it, take one every 3.3 days, on average. This works out to 27 capsules over the course of the winter, or 60 if you also take them in the fall and early spring. When you look at how little vitamin D costs, you might ask, “Can you really cure seasonal weight gain and seasonal depression for less than $5?” The answer is, “Yes, if vitamin D deficiency is the cause.” And again, about half of people are short of this vitamin.

You can get a blood test for vitamin D, but the scientific test, taking the vitamin and seeing if your condition improves, costs less. With so many people deficient in vitamin D, many experts recommend vitamin D for everyone who isn’t out in the sun, just on the chance that it might help. When you look at the costs of vitamin D compared to the costs of the diseases it helps to prevent — obesity, depression, cancer, diabetes, and others — this is a recommendation that makes a certain kind of sense.