Your body’s levels of vitamin D have diminished over the winter months. Peta Bee asks the experts why it matters to performance

Boosting your vitamin D intake is known to be good for your health, but it can also boost your fitness.

Scientists have discovered that getting enough of the sunshine vitamin – so-called because the most efficient source is the sun as it is synthesised when chemicals in the skin react to ultraviolet rays – can speed up your recovery from sessions and enhance your overall exercise performance. And, as athletes, it could be that you not only need more vitamin D to sustain repeated physical demands on your body, but you are more likely to be deficient in it in the first place.

Why your levels might be low

Dr Graeme Close, a researcher in sports nutrition and exercise metabolism at Liverpool John Moores University, says that many conventional training habits, especially during winter, compound the lack of vitamin D available to our bodies. “It’s not just that a lot of people exercise indoors more,” he says. “Even those who train outside often do so early in the morning or late in the evening. Or they wear tight compression-type clothing and a sunscreen that prevents exposure to the sun.”

Combined, these factors mean that “even using conservative guidelines” up to 70% of the recreational and serious athletes tested by Close were found to have worryingly low vitamin D levels. There is an argument, Close says, that very active people are already prone to a shortfall in certain nutrients because they are gobbled up more quickly to cope with the stress and strain of workouts.

Steve Simbler, a sports pharmacist who has worked with Olympians, says other factors might be at play. “Vitamin D is fat soluble and any that we take and don’t need is stored in body fat,” he says. “Athletes tend to have lower percentages of body fat than the average person, so it stands to reason that their ability to store it is compromised, despite the fact no clinical trials have yet proven this to be the case.”

How it affects performance

What is clear is the impact that dwindling vitamin D has on many aspects of fitness. “It is more like a steroid hormone than a vitamin in the way it acts on the body and one side-effect of low values is diminished muscle function,” Close says. “It is needed by stem cells for muscle regeneration and recovery after a hard session and there is evidence it might protect immune functions during periods of intensive training.”

So, can boosting levels reverse these risks and help you to get more out of your training in the long term? To test this, Close and his team gave a group of footballers either a vitamin D supplement or a placebo and found that, after eight weeks of training, the nutrient group showed significant improvements in two out of six fitness assessments – 10m sprint times and vertical jumps – compared to no change among their placebo counterparts.

Role in injury prevention

Perhaps the strongest evidence for workout devotees, though, comes in the form of the vitamin’s links with injury prevention and recovery. Recently, a team of exercise scientists from the University of Kentucky found that giving a vitamin D supplement to a group of swimmers, who trained predominantly indoors, seemed to offer protection against muscle injuries compared with training partners who took a daily placebo.

More than three quarters of the injuries recorded between September and March happened after a substantial drop in blood levels of vitamin D, leaving the authors to conclude “supplementation could prove to be an easy and affordable method to preserve bone and decrease risk of injury”.

How to boost your dietary intake

Nutrition scientists at the British Nutrition Foundation say that the average person needs around 10 mcg of vitamin D a day, mainly from food (children under the age of four need 7-8.5 mcg) but while fortified breakfast cereals, dairy products, egg yolks and oily fish will provide some of that intake, the vitamin is not as widely available in the diet as other nutrients.

With no clear symptoms of deficiency, the only way to tell if you are getting enough is through a blood test. But dietary steps to increase your intake will undoubtedly help.

What about supplements?

“How to get enough vitamin D is simply not that straightforward,” says Professor Dorothy Bennett, a leading vitamin D researcher and head of the molecular cell sciences research centre at St George’s University of London. “We can get it from food up to a point, but it is hard to get enough from the diet. So we need other sources and that is where it becomes controversial.”

Up to one person in three now takes the sunshine vitamin in supplement form at some time during the year; its popularity buoyed by evidence that higher levels offer greater protection against some diseases. As a fat-soluble vitamin (that is, one that
is stored in the body, such as vitamins A, D and K, as opposed to water-soluble vitamins such as vitamins B and C, which are not stored in the body and so have to be replaced), there is potential for toxicity if too much vitamin D is consumed and several studies have raised concerns about risks of high-dose vitamins, including vitamin D.

Although recent evidence suggests that even doses upwards of 10,000 IU a day of the vitamin aren’t toxic, experts recommend sticking to supplements containing 1,000 to 2,000 IU if you go down the supplement route. Young athletes, unless at noted risk of deficiency, shouldn’t need a pill.

Dr Close says that it should be taken with medical supervision or as prescribed by a dietitican and that “taking self- prescribed mega-high doses” is certainly not recommended.

And when the sun comes out?

With growing awareness about the heightened risks of skin cancer among athletes, experts remain cautious about advocating sun exposure without sunscreen.

Professor Kevin Cashman, head of the vitamin D research group at the University College Cork, says that researchers still need to pinpoint the precise levels of safe sun exposure that causes minimal skin damage but allows for vitamin D production – if, indeed, it exists.

“With the current lack of such data it is clear why sun awareness campaigns are in place,” Cashman says. “It may well be that there is no such safe level and so there may be a zero tolerance public health policy in the future.”

Professor Bennett says: “Photobiologists say 15 minutes daily of UK sun (without sunscreen) is about right and that exposure to your face and arms is all that’s needed. And children generally need less time due to their smaller body size, so aim for 10-12 minutes without sunscreen for them.”

The darker your skin, the more time you will spend longer in the sun to produce the same amount of vitamin D. Without exception, all experts agree that the skin should never be allowed to redden or burn.


Reflex Vitamin D3 Caps (£11.99; or

A super-strength dosage providing 2000 IU of the most bio-available form of vitamin D3 per capsule. Vitamin D3 is thought to be up to three times as potent as Vitamin D2. 100 capsules per bottle.

Healthspan Elite Super Strength Vitamin D3 (£9.95;

Provides 1000 IU of vitamin D3 – part of the hugely popular athlete-specific range from Healthspan. One daily tablet is recommended; 120 tablets per bottle.

Vitabiotics Ultra Vitamin D (£5.10; or

Provides 1000 IU of vitamin D3 per capsule. This product is a bargain if you want to try supplements.