Vitamin D is all the rage at the moment. Everyone is measuring it and no one, it seems, is getting enough of it. Of course, Vitamin D is not really a vitamin because dietary intake is usually not required to maintain healthy levels, unless you wear a burqa.
By getting adequate sun (UV-B) exposure, your skin can make all the vitamin D you need to stay healthy. It is then stored in your liver and fat for later use.
That’s why vitamin D levels are naturally lower in winter and spring, and at their highest in summer and autumn. It’s also why getting your stores up in the warm light of summer is important to get through a dark winter, rugged up and indoors.
The problem is that skin cancers and four out of every five wrinkles are also caused by solar radiation. So every time we slip, slop and slap to reduce the negative effects of sunlight, we also reduce the vitamin D that can be made by our skin. Sunscreen with a sun protection factor (SPF) of 15 or more blocks most of the vitamin D synthesis underneath the sun-blocked skin.
But sunblock is not our biggest barrier to getting enough vitamin D. Most people don’t apply enough sunscreen, don’t cover all sun-exposed skin, and don’t regularly reapply.
The bigger issue is that we are not getting outside, period. To get our vitamin D, we should aim for a regular dose of sunlight every day. Even 10 minutes can be enough. Better still, combine it with moderate intensity physical exertion. UV-B does not penetrate glass, so just looking out at a sunny day isn’t enough.
Low vitamin D levels are obviously most common in those who stay indoors too long, which, quite frankly, is most of us sedentary office workers. Special at-risk groups include the obese, the institutionalised, the frail, and the elderly. Having dark skin which scatters ultraviolet light also contributes to low vitamin D stores.
People with diabetes tend to have lower levels, as vitamin D is lost into the urine in patients with albuminuria. People with kidney or liver disease, malabsorption and those taking certain drugs (e.g. anticonvulsants, some anti-HIV treatments) are also at increased risk.
Our bodies probably work best when levels vitamin D are greater than 75 nanomolar. It is now thought that over half of all adults probably have inadequate vitamin D stores (less than 50 nanomolar on a simple blood test ) with up to a quarter dropping to significantly low levels during the colder months (less than 25 nanomolar).
When vitamin D levels are low, the body signals the release calcium stored in our bones. This leads to progressive thinning of the bones, loss of muscle strength, and an increased risk of fracture. When vitamin D stores are low some people complain of body or muscle aches and pains.
Low levels of vitamin D have also been associated with an increased risk of cardiovascular disease, diabetes, multiple sclerosis and some cancers. But it is hard to know whether vitamin D increases the likelihood of developing these diseases, or whether the causes of low vitamin D (like being sedentary indoors and not getting enough exercise) are actually to blame.
A key question is whether taking moderate to high doses of vitamin D can prevent these serious health problems? Some clinical trials say yes, while others say no. When you put them all together, the effects of vitamin D supplements are modest at best.
The benefits of supplementation are probably not significant when compared with other measures an individual can make to improve their health. In the same way that an orange is more than just vitamin C, outdoor exercise outperforms a vitamin D capsule every time.
If you are not getting enough sun, or have increased requirements, then it comes down to what you eat or how you can supplement your diet.
In food, the highest levels of vitamin D are found in oily fish such as trout, salmon, mackerel, herring, sardines, anchovies, pilchards, and tuna. These are naturally rich in all sorts of health-promoting chemicals, like omega-3 fatty acids and vitamin D. Processed fish (canned tuna, salmon, etc) has about half to a third less vitamin D than cooked, fresh fish.
Fish oil and fish liver oils like cod-liver oil contain much more vitamin D. In fact, a tablespoon of cod-liver oil twice a week provides almost all your vitamin D requirements.
Other foods that contain small amounts of vitamin D include cheese, meat, egg yolks and wild mushrooms, but none come close to providing what you need to maintain healthy levels. Vitamin D is also available in fortified products such as cereals, juice, bread and some milk, which can be a good alternative to supplements.
Most adults get less than a quarter of the vitamin D they need from their diet. To make up the difference, vitamin D supplements are a best seller.
A number of different supplements are available that include vitamin D2 (ergocalciferol from yeast) or vitamin D3 (cholecalciferol from fish or lanolin). Vitamin D2 is a little less potent, so is generally taken in slightly higher doses. Most will contain your total daily requirements of vitamin D in a single capsule (about 20 to 25 micrograms).
Because vitamin D is stored, high-dose oral therapy (weekly or monthly) or intramuscular injections of vitamin D can be a practical alternative for some people, although both are probably less effective than regular daily use.
Obviously, the doses of vitamin D required to raise low levels back into the healthy range are much greater than those needed to keep them there. In those with people with really low levels, taking ten times more than normal daily requirements (about 250 micrograms a day) every day for two to three months will usually restore their stores.
This may seem a lot, but it is no more than a summer at the beach. Once levels are restored, once capsule a day is usually enough to maintain your levels.
As supplements go, Vitamin D is generally safe and well tolerated. The body is used to storing large quantities of vitamin D but there are risks to taking more than the recommended levels.
If you don’t drink enough fluid each day, your risk of kidney stones can increase. Excessive doses might also promote calcification of arteries in those with diabetes or kidney disease who are already prone to this type of calcification.
While the links between low levels and vitamin D and disease are becoming increasingly clear, we still don’t know whether vitamin D deficiency is a symptom or a cause. If you are diagnosed with low levels of vitamins D, think of it as a nudge to evaluate your overall health and consider getting some outdoor exercise.