How much sunshine is good for you?
For decades, sunlight was associated with good health. But rising skin cancer rates have changed how experts view sun exposure.
Moderate exposure to sun can still provide health benefits, but the amount needed varies depending on skin type, location and cancer risk, according to the BBC.
The popularity of tanning grew in the 1920s after photographs of Coco Chanel returning from a Mediterranean cruise with a tan helped make bronzed skin fashionable. In the early and mid-20th century, sunlight therapy was also used to treat conditions such as rickets and tuberculosis.
Today, excessive sun exposure is known to increase the risk of skin cancer. However, research suggests that limited exposure can support vitamin D production, mental health, sleep and cardiovascular health.
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Why do we need sunlight?
Sun exposure helps the body produce vitamin D, which is important for healthy bones and muscles. Adequate vitamin D levels may also help regulate the immune system and reduce inflammation.
Sunlight can also affect blood pressure. UVA rays can trigger the release of nitric oxide, which helps blood vessels widen and may reduce the risk of heart attacks and strokes.
Daylight also plays an important role in sleep and cognitive health. Morning light helps regulate the body's internal clock by increasing cortisol and reducing melatonin.
Greater exposure to daylight has been linked to better cognitive performance, reaction times and memory. One study involving more than 360,000 people found that around 1.5 hours of daytime sunlight exposure was associated with a lower risk of dementia.
Sunlight can also increase serotonin levels, which may improve mood and focus. Limited exposure to daylight, meanwhile, has been associated with depressive symptoms, low mood and insomnia.
How much sunlight is enough?
According to the BBC, experts generally recommend short and regular periods of exposure rather than prolonged time in the Sun.
Rebecca Mason, a professor of physiology at the University of Sydney, says sunlight is most effective for vitamin D production around the middle of the day, when UVB levels are highest.
For people with light skin, Mason recommends exposing the hands, arms or legs for a few minutes at a time on most days. In areas with very high UV levels, this should instead be done in the mid-morning or mid-afternoon.
People with darker skin may need more exposure because higher levels of melanin slow vitamin D production. One study found that people with dark brown skin in the UK needed about 25 minutes of midday exposure during spring and summer to produce adequate vitamin D.
People with very pale skin, many moles or a personal or family history of melanoma face a higher risk of skin cancer and need to take greater precautions. The same applies to people taking immunosuppressants.
The balance between the benefits and risks of sunlight also depends on skin type and UV levels. Darker skin provides greater protection against UV-related DNA damage, while lighter skin can be vulnerable even at low UV levels.
What are the risks of too much Sun?
Spending longer in the Sun does not continue to increase vitamin D production. It does, however, raise the risk of sunburn, pigmentation, premature ageing and skin cancer.
According to the BBC, melanoma cases in the UK have exceeded 20,000 a year for the first time. Cancer Research UK estimates that about nine in 10 cases are preventable and links excessive UV exposure and sunbed use to the disease.
Too much sunlight can also damage the eyes and cause cataracts. Doctors recommend sunglasses with UV 400 lenses to protect against harmful rays.
Sun protection is particularly important during childhood and adolescence, as exposure during the first 20 years of life can significantly affect the later risk of skin cancer.
What happens if we get too little sunlight?
People who live in areas with limited sunlight may develop low vitamin D levels, especially during winter. Those with darker skin, limited access to the outdoors, photosensitivity or skin-covering practices may also face a higher risk of deficiency.
Long-term vitamin D deficiency can contribute to bone conditions such as rickets and osteomalacia. However, vitamin D deficiency can generally be treated with supplements.
In countries with limited winter sunlight, including the US and Canada, some foods are fortified with vitamin D.
Experts also warn against excessive supplementation. Taking more than 4,000 IU, or 100 micrograms, of vitamin D a day is widely considered harmful because it can cause high calcium levels, potentially weakening bones and damaging the kidneys and heart.
Ultimately, experts say only small to moderate amounts of sunlight are needed for good health. Prolonged unprotected exposure should be avoided, while short periods of outdoor activity can provide the benefits of daylight without unnecessarily increasing the risks.
