Everyone loves a sunny day. As a species, we could easily be classified as sunbathers. That could be because we humans, the species called Homo sapiens sapiens (meaning ‘wise, wise man’ – so wise they named us twice), evolved in Africa, where there is plenty of sunshine.
When our ancestors left Africa about 70,000 years ago, they moved to places where the sun still shone a lot. After all, they came to Ireland about 10,000 years ago and the mystery is why did they stay? It probably wasn’t the weather.
But we still get a few nice sunny days. Especially in July and August. As Mundy 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 plenty 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 get sunburned or overexposed to the sun because of the risk of cancer, but a little sunlight can do wonders.
Recently, sunshine has been shown to increase appetite and help you gain weight, but only if you’re male – more on that later.
Sunlight is important for maintaining vitamin D levels in your body. Vitamin D is formed in your skin when exposed to UV light, which occurs in sunlight. I bet you never would have guessed that when the sun shines on your skin, a natural chemical reaction occurs and that the chemistry makes vitamin D.
If you’re reading this in the sun, look down at your skin and think of all the chemistry that’s going on. I notice that 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 than ever in these Covid times.
Sunlight is also good for mood. During 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 levels of serotonin in your body, which benefits your mood. This is what some antidepressants do, so sunlight is a bit like natural Prozac.
Sunlight can also help you sleep better. It has been shown that an hour of natural light in the morning can regulate your internal clock and ensure that you produce melatonin at the right time in the evening.
Melatonin is the body’s natural sleep aid and helps you fall asleep. Sunlight in the morning starts the melatonin clock winding up, with melatonin being released just before bedtime.
And there’s more evidence that sunlight is good for you. A study of 30,000 Swedish women showed that those who spend more time in the sun live up to two years longer than those who don’t.
This could be partly because you’re spending more time outdoors and probably getting more exercise, but whatever the reason, a little bit of sunlight can extend your life.
And sunlight has been shown to lower blood pressure and protect your heart, both of which prolong life.
Sunlight has now been found to improve your appetite after 3,000 people took part in a study of diet and weight gain. Scientists made the remarkable finding that men, but not women, increase the amount of food they eat in the summer, which in turn could lead to weight gain.
Then they exposed male and female subjects to the midday sun for 25 minutes. They found that this increased blood levels of a hormone called ghrelin in men, but not in women for some reason.
Ghrelin is also called the hunger hormone because it makes you hungry. Just before a meal, the level of ghrelin in your blood rises. It goes into your brain and causes that familiar feeling of hunger. Ghrelin returns to normal after eating.
It seems to work in part by increasing the movement of your stomach — those rumbling sounds you hear when you’re hungry — and also stimulating your stomach to form acid in anticipation of the food you’re about to eat, since the Acid aids digestion.
The observation that ghrelin levels rise 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 like lots of evidence), the scientists exposed mice to UV light. And guess what? Again there was an increase in ghrelin, but again only in males. The male mice ate more and were more motivated to search for food.
What caused the ghrelin to be released? The scientists tracked it down to minor damage in the skin, particularly damage to fat cells. The skin has a layer of fat cells whose main job is to provide insulation. A bit like a built-in coat. The slight damage led to the release of ghrelin from the damaged fat cells.
Ghrelin has other effects on the body, including suppressing inflammation. It could therefore be made to protect the damaged skin and block inflammation.
Ghrelin can also protect the heart, and so the increase in ghrelin may help explain why sun exposure has a protective effect on the heart. Although men may be eating more, which could put them at risk for heart disease, they also made ghrelin to protect the heart.
The scientists wondered why there was no effect in women. It could be the estrogen. Not only is estrogen the main hormone that regulates the female reproductive system, but it can also protect the body in a number of ways. It can block the damage caused by sunlight to the fat cells in the skin, preventing ghrelin from being triggered.
This study 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.
The recommended duration varies widely based on factors such as skin tone and color, how close you are to sea level, or how close you are to the equator. It is important to protect your skin from too much sun exposure by applying the sunscreen.
The sunlight study is of great interest to scientists working on appetite, as lack of appetite can be a problem in the elderly or in people with cancer.
A short exposure to the sun might well help. It also reinforces the idea of giving someone ghrelin to stimulate their appetite and allow them to maintain their weight.
Whichever way you look at it, a little sunshine does you very well, so make the most of the nice weather this weekend, in a safe way. It will help your mood, sleep, bones, immune system, heart and, if you are a man, give you a healthy appetite.
Heed Mundy’s advice: “July, bubble bombs in my mouth.”
Luke O’Neill is Professor of Biochemistry in the Department of Biochemistry and Immunology at Trinity College Dublin
https://www.independent.ie/opinion/comment/here-comes-the-sun-natures-answer-to-prozac-41845484.html Here comes the sun, nature’s answer to Prozac