Sunlight is the simplest source of vitamin D, and also one of the most misunderstood. Some people avoid the sun completely, others try to soak up as much as possible. The truth sits in the middle, and it depends on where you live, how you dress, and your own skin.
What vitamin D does
Vitamin D helps your body absorb calcium and phosphorus, which keeps bones and teeth strong. It also plays a role in muscle function and the immune system. Unlike most vitamins, your body can make it, when ultraviolet B (UVB) rays from the sun reach your skin. Food provides some too, but sunlight is the main natural source for many people.
How sunlight makes vitamin D
When UVB light hits your skin, it starts a chain of reactions that produces vitamin D. Your body then stores it and converts it into its active form through the liver and kidneys. You can’t make vitamin D from sunlight passing through window glass, because glass blocks most UVB.
What affects how much you make
- Latitude and season. Far from the equator, in winter, the sun is too low for much UVB to reach the ground.
- Time of day. UVB is strongest around midday and weak in early morning and late afternoon.
- Skin tone. Melanin, the pigment that darkens skin, reduces UVB absorption, so people with darker skin generally need longer sun exposure to make the same amount.
- Age. Older skin makes vitamin D less efficiently.
- Clothing. Skin that’s covered can’t make vitamin D. Anyone who wears clothing covering most of the body, for religious, cultural, or workplace reasons, may get far less from sunlight and should pay more attention to other sources.
- Sunscreen. It reduces UVB reaching the skin, though most people don’t apply it perfectly, so some vitamin D is still made.
- Cloud, pollution, and time indoors. All reduce exposure.
How much sun is enough?
There isn’t a single number. Recommendations vary between countries and depend on season, location, and skin type. Many health authorities suggest short, regular exposure of the face, arms, or hands during the sunniest part of the day, often just a few minutes to around a quarter of an hour for lighter skin in summer, and longer for darker skin. The key is not to reach the point of burning or reddening.
Your best guide is the advice of your national health service or your doctor, since the right amount depends on where you live.
Balance vitamin D with skin protection
Too much sun damages skin and raises the risk of skin cancer, so more exposure isn’t better. Once you’ve had a short, sensible dose of sunlight, protect your skin: seek shade, wear a hat and clothing, and use sunscreen when the UV index is high. You don’t need to burn or tan to get vitamin D. Deliberate tanning isn’t a healthy strategy.
Food sources of vitamin D
Few foods contain much vitamin D naturally, but some help:
- Oily fish such as salmon, sardines, and mackerel.
- Egg yolks.
- Some mushrooms, particularly those exposed to UV light.
- Fortified foods, such as certain milks, cereals, and spreads, depending on your country.
Check labels to see whether products are fortified. For many people, diet alone doesn’t supply enough, especially in winter.
Who may be at higher risk of low vitamin D
- People who spend most of their time indoors.
- Those with darker skin, especially living in northern climates.
- People who cover most of their skin outdoors.
- Older adults.
- Infants who are exclusively breastfed, unless advised otherwise by a health professional.
- People with certain medical conditions that affect absorption.
- Those living far from the equator during autumn and winter.
Signs of low vitamin D
Low vitamin D often causes no obvious symptoms. When it’s severe or prolonged, it can lead to bone pain, muscle weakness, and soft bones. These symptoms have many other possible causes, so don’t assume a low level from tiredness alone. A blood test ordered by a doctor is the only reliable way to check.
What about supplements?
Many people use vitamin D supplements, particularly in winter, and some health authorities recommend them for specific groups. But more isn’t better. Very high doses over time can cause harmful effects, such as too much calcium in the blood. The right dose depends on your age, diet, health, and test results, so speak to a doctor or pharmacist before starting, especially if you’re pregnant, take other medication, or have a chronic condition.
Practical habits
- Spend some time outdoors in daylight most days, ideally around midday in spring and summer.
- Take a short walk at lunchtime instead of eating at your desk.
- Include oily fish, eggs, and fortified foods in your meals.
- Protect your skin once you’ve had a short exposure.
- Ask a doctor about testing if you’re in a higher-risk group.
Common myths
- “Sitting by a sunny window counts.” Glass blocks most UVB, so it doesn’t.
- “Sunscreen causes deficiency.” Studies suggest normal use has a limited effect on vitamin D status, and skin cancer protection matters.
- “You can store up in summer for the whole winter.” Levels do carry over for a while, but they gradually fall.
- “Everyone needs a supplement.” Not necessarily. Needs vary.
FAQ
Can I get enough vitamin D in winter?
In regions far from the equator, it’s difficult, and diet or supplements may be needed. Ask a health professional what’s right for you.
Do I need sun on my whole body?
No. Exposing the face, hands, or arms for a short time is usually the practical approach.
Is cloudy weather useful?
Some UVB passes through clouds, but less. Time outside is still helpful for general wellbeing.
Is vitamin D important for children?
Yes, for growing bones, but dosing for children needs medical guidance.
The takeaway
Short, regular, sensible sun exposure, plus a diet that includes vitamin D sources, covers the needs of many people. If you’re in a higher-risk group, ask about testing rather than guessing. This article is general information, not personal medical advice.
