Vitamin D plays a vital role in:

1. Bone and muscle health

Helps the body absorb calcium.
Keeps bones strong and reduces the risk of stress fractures (particularly important for adolescents and athletes).
Supports normal muscle function.

2. Immune system support

Vitamin D helps your immune system respond effectively, reducing susceptibility to infections — something athletes particularly feel during heavy training blocks.

3. Hormonal and mood regulation

Low levels have been linked with low mood, fatigue, and hormonal disruption, including issues related to low energy availability.

4. Overall health

It plays a role in inflammation regulation, cardiovascular health, and long-term wellbeing.

How Do We Make Vitamin D?

Your body makes vitamin D when UVB rays from sunlight hit your skin. But UVB rays are only strong enough at certain times of the year.

If your shadow is shorter than you, UVB rays are strong enough for your skin to produce vitamin D. If your shadow is longer than you, UVB rays are too weak.

Vitamin D in the Summer

For the fact that we rely on UVB rays to produce Vitamin D, it is crazy how complicated it can be to get it. From late March to early October in the UK, UVB light is strong enough to produce vitamin D — but only during the middle of the day.

How much time do we need outside?

It varies depending on skin tone, age, and how much skin is exposed, but as a general guide:

10–20 minutes of midday sun exposure to arms and legs for lighter skin tones.
20–40 minutes (or longer) for medium to darker skin tones.

This does not mean sunbathing or burning — short periods of daily exposure are enough.

Top tips for getting vitamin D in summer

Use the shadow rule to check if vitamin D production is possible.
Get outside around midday for short periods.
You can still wear sunscreen — real-world evidence suggests typical sunscreen application doesn’t block production as we accidentally leave sections exposed.
Build vitamin D naturally before autumn arrives, as your body can store some.

Vitamin D in the Winter

From October to early March, UVB rays in the UK are too weak to produce vitamin D — even on sunny days.

That means everyone is at risk of low levels, but especially:

Teenagers
Athletes and high-training-load individuals
People with darker skin
Anyone who spends most of the day indoors

How to get vitamin D in winter

Food sources:

Oily fish (salmon, mackerel, sardines)
Egg yolks
Fortified foods (cereals, dairy alternatives, yoghurts)
Mushrooms exposed to UV light

But diet alone rarely provides enough — even perfect diets typically cover just 10–20% of needs.

Winter supplementation

The NHS recommends:

10 micrograms (400 IU) daily for everyone during autumn and winter.
Athletes may benefit from more, depending on training load, bone health, or previous levels — but this should be guided by a dietitian or healthcare professional.
The International Olympic Committee recommends a daily dose of 1,000–2,000 IU (International Units) of vitamin D3, so significantly higher than the NHS recommendations
For athletes with low energy availability or menstrual dysfunction, combined calcium (1500 mg/day) and vitamin D (1,500–2,000 IU/day) intake is specifically recommended to optimise bone health..

Why Vitamin D Matters for Athletes and Active Individuals

Athletes often have higher vitamin D needs due to:

1. Increased bone turnover

Heavy training — especially running, dance, gymnastics, and football — increases stress on bones. Low vitamin D levels raise the risk of:

Bone injuries
Stress fractures
Poor recovery

2. Muscle strength and power

Vitamin D supports healthy muscle function, reaction time, and neuromuscular performance.

3. Immune resilience during heavy training

Low vitamin D is linked with:

Higher rates of colds and respiratory infections
Slower recovery from illness

4. Energy and wellbeing

Low vitamin D can contribute to fatigue and low mood — both of which impact motivation and training consistency.

How to choose a Vitamin D supplement

1. Batch tested

Make sure you choose a brand that has third party testing, e.g. Thorne’s Vitamin D or Healthspan’s Elite Vitamin D.

2.Spray, drops or capsules

Sprays and drops have better overall absorption

3. Dosage

Decide on dosage based on your requirements. This could be dependent on a blood test, whether you train mostly indoors or whether you are currently recovering from low energy availability or RED-S.

4. Routine

Make it part of your routine. I have a spray above my coffee machine as I make a cup of coffee every morning so this helps me remember to take it. The more you link it to another routine that you already have established, the more likely you will be to make it part of your new routine

Final Thoughts

Vitamin D is one of the simplest nutrients to optimise — yet deficiencies are so common, especially among active individuals and teenagers. Being proactive in both summer and winter can support your: