Vitamin D in the UK: what people who train need to know

What the NHS recommends

The NHS advice for adults is straightforward:

• Autumn and winter: everyone should consider taking a daily supplement containing 10 micrograms of vitamin D, which is the same as 400 IU.
• Spring and summer: most people can get enough from sunlight and a balanced diet, so a supplement is optional.

Some people are advised to consider taking 10 micrograms a day all year round, because they are unlikely to make enough from sunlight even in summer:

• People who are not often outdoors, such as those who are frail or housebound
• People who live in a care home
• People who usually wear clothes that cover most of their skin when outdoors
• People with dark skin, for example from an African, African-Caribbean or south Asian background

Babies, children, and pregnant and breastfeeding women have their own guidance, so check the NHS website or ask a midwife, health visitor or pharmacist.

Vitamin D and training

Vitamin D helps your body absorb calcium and phosphate, which keep bones, teeth and muscles healthy. Severe deficiency in adults can cause bone pain and muscle weakness, a condition called osteomalacia. For anyone doing weight-bearing training, running or jumping, healthy bones are part of staying injury-free, alongside the benefits of strength training for bone health.

There has been a lot of interest in vitamin D and athletic performance. The fairly clear picture is that correcting a deficiency can help muscle function and general health, but taking extra when your levels are already adequate does not seem to improve strength, speed or endurance. It is about avoiding a shortfall, not finding an edge.

If you train at a 6am class through the winter, you may barely see daylight on weekdays. That makes the supplement even more relevant. The same goes for shift workers and anyone with an indoor job.

Food sources

Food will not usually cover your needs in winter, but it helps. Good sources include:

• Oily fish such as salmon, mackerel, sardines, herring and trout
• Egg yolks
• Red meat and liver (liver is high in vitamin A, so pregnant women should avoid it)
• Fortified foods, including some breakfast cereals, fat spreads and plant-based milks and yoghurts
• Some mushrooms that have been exposed to UV light, which will say so on the pack

Eating oily fish once or twice a week, as the NHS recommends, gives useful amounts of vitamin D along with omega-3. See fats in your diet for more on oily fish.

Choosing a supplement and staying safe

A basic supplement providing 10 micrograms is all most people need, and supermarket and pharmacy own brands are usually fine. Vitamin D3 is the most common form. Many D3 supplements are made from lanolin in sheep's wool, so vegans should look for lichen-based D3 or vitamin D2.

More is not better. The NHS advises adults not to take more than 100 micrograms (4,000 IU) a day, as too much over a long period can cause calcium to build up in the body, which can weaken bones and damage the kidneys and heart. Some online products contain very high doses, so check the label.

People with certain conditions, such as kidney disease or sarcoidosis, or who take some medicines, should check with their GP or pharmacist before taking vitamin D.

Getting vitamin D from summer sun safely

From late March to the end of September, most people in the UK can make enough vitamin D from being outdoors. The NHS says short daily periods of sun on uncovered skin, such as forearms and hands, are enough for most people, without needing to sunbathe. People with darker skin need longer in the sun to make the same amount.

The balance is avoiding sunburn, which raises the risk of skin cancer. Cover up or use sunscreen before your skin starts to turn red or burn, and take extra care between 11am and 3pm in summer. A walk at lunchtime, training outdoors when you can and getting outside at weekends all help.

Sitting by a sunny window does not work, because glass blocks most UVB. Neither do sunbeds, which the NHS advises against because of the skin cancer risk.

Should you get tested?

Routine testing is not needed for most healthy adults, because the simple advice to supplement in winter covers the majority of people. Your GP may test your levels if you have symptoms such as bone pain, muscle weakness or unexplained tiredness, or if you are in a higher risk group.

Tiredness has many causes, including poor sleep, low iron, stress and under-eating, so it is worth seeing your GP rather than assuming it is vitamin D. Our guides to iron and training and sleep for recovery cover some of the other common culprits. If you want company for training through the darker months, the free trial at Lycan Strength is an easy way to start.