Exposure to sunshine at this time of year not only lifts our mood but also strengthens our bones.
Yet although modern life is much more comfortable and convenient – light at the flick of a switch; warm, dry workplaces; weatherproof vehicles – our bodies are designed to live in a different way. They need regular exposure to outdoor light to function properly.
International studies suggest we spend 90% or more of our time inside and that’s taking a toll on our health, sleep and mood.
The good news is it’s possible to offset the effects of our indoor lifestyle without having to live like our ancestors did. Going outside after breakfast can help regulate sleeping patterns all year round, and getting some winter sun in the middle of the day can boost flagging vitamin D levels. Sunlight may also lift our mood. Several studies have found that people have higher levels of serotonin – a brain chemical linked to mood – on sunny days than on cloudy ones.
Our bodies make vitamin D when our skin is exposed to the ultraviolet B (UVB) rays in sunlight. Vitamin D is important for strong, healthy bones because it helps us absorb calcium and it also helps boost our immune system.
Low levels of vitamin D are associated with a wide range of other health problems, including autoimmune diseases such as type 1 diabetes and multiple sclerosis, cancer and allergies. Pamela Von Hurst, who is co-director of Massey University’s vitamin D centre, says the list is constantly increasing.
“I’ve just come back from an international vitamin D workshop in Spain and the work being done is really interesting – all sorts of health conditions are being considered.”
A study published in the journal BMJ last year, for example, found that giving supplements to people who are vitamin D-deficient can help protect them from respiratory illness. Another study, published in Bone Research, found that supplements improved the pregnancy outcomes of African-American women – a group Von Hurst says are “notoriously vitamin D-deficient” because their darker skin makes it harder for them to make the vitamin.
“The supplements meant they had fewer small-for-gestational-age babies. They also reduced preterm labour, gestational diabetes and gestational hypertension.”
Most of us start the winter with good levels of vitamin D, but they soon start to fall as the days get shorter and we spend less time outside. Von Hurst says getting regular winter sun in the middle of the day – when UVB levels are highest – can help us maintain our vitamin D levels.
In northern parts of the country, that’s easy, with two to three hours’ exposure a week, preferably wearing a short-sleeved top. Further south, where UVB levels are much lower during winter, it may be worth taking vitamin D supplements.
Exposure to outdoor light is also important to help us sleep, with the most effective time being about an hour after waking up. Lora Wu, a senior research officer at Massey University’s sleep-wake centre, says that switches off the production of melatonin, the hormone that helps control our circadian rhythm – the 24-hour internal clock that governs our sleep/wake cycle. Switching it off in the morning helps us stay awake and alert during the day; we start producing it again in the evening as it gets darker and we get ready to sleep.
“There are critical periods in your circadian rhythm where a little bit of light exposure can go a long way. Exposure during the afternoon doesn’t affect your sleep so much.”
As to how much morning exposure you need, estimates range from 15 minutes to 45 minutes. It’s also possible to get some of the benefits of outside light from sitting next to a window. The intensity of the light is much lower – about 3000 lux compared with 10,000 lux or more outside – but it has some of the same effects.
“There’s some research that suggests people who have a window in their office during the day sleep better and have better moods, so it may be possible to get the benefits of bright light without necessarily being outside,” says Wu.
Ideally, though, we should spend as much time outside during the day as possible. “You should get out and get more light because it’s really helpful.”
This article was first published in the June 16, 2018 issue of the New Zealand Listener.