Everyone loves a sunny day. As a species, we could best be classified as sunbathers. This may be because we humans, the species called Homo sapiens sapiens (meaning “wise wise man” – so wise they mentioned us twice), evolved in Africa, where there is a lot of sunshine.
When our ancestors left Africa about 70,000 years ago, they moved to places where the sun was still shining. Finally, about 10,000 years ago they came to Ireland, and the mystery is why they stayed? It couldn’t be the weather.
But we still get some nice sunny days. Especially in July and August. As Mundy so famously sings in his song July: “Looks like another perfect day/July, please do your best to stay.” And this July is no different, with lots of sunshine last week.
And the good news is that sunshine is good for you in many ways. You have to be careful not to burn yourself or get too much sunlight because of the risk of cancer, but a little sunlight can work wonders.
It has recently been shown that sunshine can stimulate your appetite and help you gain weight, but only if you’re a man – more on that later.
Sunlight is important for maintaining vitamin D levels in your body. Vitamin D is made in your skin when it is exposed to UV light, which occurs in sunlight. I bet you never thought that a natural chemical reaction takes place in your skin when the sun shines on it, and that chemistry makes vitamin D.
If you’re reading this in the sun, look at your skin and think about all the chemistry that’s going on. This strikes me when I look at my skin, but then I’m a nerd. Vitamin D is essential for strong bones and also helps your immune system, which we are more aware of in these Covid times.
Sunlight is also good for your mood. In the winter, some people get what’s called seasonal affective disorder, or SAD. It is a form of depression that can be relieved by UV light.
Sunlight increases the level of serotonin in your body, which helps your mood. This is what some antidepressants do, so sunlight is a bit like natural Prozac.
Sunlight can also help you sleep better. An hour of natural light in the morning has been shown to regulate your biological clock so that you produce melatonin at the right time in the evening.
Melatonin is the body’s natural sleeping pill and helps you fall asleep. Sunlight in the morning winds up the melatonin clock, releasing the melatonin just before you go to bed.
And there’s even more evidence that sunlight is good for you. A study of 30,000 Swedish women found that those who spent more time in the sun lived up to two years longer than those who didn’t.
This may be partly because you spend more time outdoors and probably exercise more, but whatever the reason, a little sunlight can extend your life.
And sunlight has been shown to lower blood pressure and protect your heart, both of which will extend life.
It has now been discovered that sunlight can help your appetite, after 3,000 people took part in a study on diet and weight gain. Scientists came to the striking finding that men, but not women, increased the amount of food they ate during the summer, which in turn could lead to weight gain.
They then exposed male and female volunteers to 25 minutes of afternoon sun. They found that this increased the level of a hormone called ghrelin in the blood of men, but for some reason not in the women.
Ghrelin is also called the hunger hormone because it makes you hungry. Just before a meal, the ghrelin level in your blood rises. It goes to your brain and causes that familiar feeling of hunger. Ghrelin returns to normal after you eat.
It seems to work in part by increasing your stomach’s movement — those grumbling sounds you hear when you’re hungry — and also stimulates your stomach to make acid in anticipation of the food you’re about to eat, as the acid aids digestion. promotes.
The observation that ghrelin levels went up after sunlight therefore provided a mechanism for how sunlight might stimulate appetite. Mechanism is everything when it comes to science.
To get more evidence (remember, scientists love a lot of evidence), the scientists exposed mice to UV light. Guess what? Again there was an increase in ghrelin, but again only in the men. The male mice ate more and were more motivated to forage for food.
What released the ghrelin? The scientists followed it for mild damage in the skin, especially damage to fat cells. The skin has a layer of fat cells, the main job of which is to provide insulation. Kind of like a built-in jacket. The mild damage led to the release of ghrelin from the damaged fat cells.
Ghrelin has other effects on the body, including suppressing inflammation. It can therefore be made to protect the damaged skin and block the inflammation.
Ghrelin may also protect the heart, so the rise in ghrelin may help explain why exposure to sunlight has a protective effect on the heart. While men may eat more, putting them at risk for heart disease, they also made ghrelin to protect the heart.
The scientists wondered why there was no effect in women. This could be due to estrogen. In addition to being the main hormone that regulates the female reproductive system, estrogen can protect the body in several ways. It can block the damage caused by sunlight to the fat cells in the skin and thus prevent the activation of ghrelin.
This research gives us even more insight into what happens when the sun shines on us. However, it is important to be careful in the sun. Moderate exposure is key – 10 to 30 minutes of midday sun, but no more than that.
The recommended length of time varies widely, due to things like skin tone and color, how close you are to sea level, or how close you are to the equator. It’s important to protect your skin from too much exposure by slathering on the sunscreen.
Sunlight research is of great interest to scientists working on appetite, as loss of appetite can be a problem in older people or those with cancer.
Brief exposure to sunlight may help. It also adds weight (get it?) to the idea of giving someone ghrelin to stimulate their appetite, helping them maintain their weight.
Whichever way you look at it, a little sun is very good for you, so take advantage of the beautiful weather this weekend in a safe way. It will help your mood, your sleep, your bones, your immune system and your heart, and if you are a man, it will give you a healthy appetite.
Take Mundy’s advice: “July, bombs in my mouth.”
Luke O’Neill is Professor of Biochemistry at the School of Biochemistry and Immunology at Trinity College Dublin