Summer is on the way, and many of us will start reaching for the sunscreen. Protecting our skin from sun exposure is important not just to prevent premature skin ageing (although keeping wrinkles at bay is good) but also to protect against skin damage that can lead to skin cancer. However, exposure to sunlight is also vital for producing vitamin D, which is essential for good bone health, boosting our immune system and a whole host of other health benefits. So, how much sun exposure do we need to produce enough vitamin D, and does using high-SPF sunscreen block or impair the skin’s ability to make it?
For most people, their principal source of vitamin D is through exposure to sunlight on the skin. In the UK we can only make vitamin D from April to October, so in the winter months it is advised to take a supplement to keep levels topped up. Some foods—such as eggs, oily fish, and fortified products—are high in vitamin D, but it can be difficult to get enough through diet alone. So, come the warmer months, it’s beneficial for our health to ensure we are getting regular skin exposure to sunlight. The UVB rays in sunlight penetrate the upper layers of skin and convert a compound in the skin (7-dehydrocholesterol) into pre-vitamin D3, which is in turn converted into vitamin D in the body.
Vitamin D is essential throughout life to maintain good bone health. A lack of it in children can affect bone growth, leading to rickets, while in adults it can lead to conditions such as osteoporosis. Vitamin D deficiency can also result in fatigue, muscle weakness, reduced immune function, and low mood.
Vitamin D deficiency is quite common in the UK, especially during the winter months and particularly among people with darker skin, people who do not get enough sunlight (for example, due to reduced mobility and being inside), and those who cover their skin for religious reasons—or simply due to a general lack of outdoor activity.
Whilst sun exposure is recommended for boosting vitamin D, we are also advised to use sunscreen to protect our skin from sun damage. So, how long do we need in the sun to make vitamin D, and do sunscreens block UVB rays, preventing us from producing it?
Studies have suggested that little and often is the best approach to keep vitamin D levels topped up. The amount of time will vary depending on the sun intensity, amount of skin exposed and skin colour. For lighter skin, 10–15 minutes of sun exposure on a reasonable area of skin (e.g., face, arms and lower legs) should provide enough vitamin D; for darker skin tones, more exposure is needed—around 25–40 minutes—because higher melanin in darker skin types reduces vitamin D production.
Sunscreens are designed to filter out UV radiation, including UVB, so theoretically they should lower vitamin D production. However, researchers have shown that not all sunscreens completely block UVB rays. This is often because sunscreen is not applied thickly enough or is not reapplied frequently, meaning some UVB still reaches the skin. Additionally, not all sunscreens are equally effective at blocking UVB rays. So, if you are out in the sun for a long period, the sunscreen should hopefully protect your skin from sunburn, but some UVB rays will get through and boost vitamin D production.
If you are concerned about vitamin D levels, one option is to get some unprotected sun exposure for 15–20 minutes, then apply sunscreen. The best time to make vitamin D is between 11am and 3pm, when the sun is at its highest and UVB rays are strongest. However, people with lighter skin may want to avoid exposure around midday when the sun is at its strongest to avoid sunburn.
In general, expert advice is that balancing vitamin D production with sun safety is best achieved through a “little and often” approach. Around 20–30 minutes of sun exposure should help maintain vitamin D levels.
Enjoy the sun.
Rachel Kayani, Science Tutor and Writer
