What does sunshine do to our brains?

RTÉ News​

17-05-2025

We're certainly making up for the lousy weather we've seen so far this year with days of endless sunshine and blue skies. While it's a boost to morale and puts more of a pep in our step, what does sunshine do to our brains? Dr Ruth Freeman from Science Foundation Ireland joined The Business on RTÉ Radio 1 to discuss this matter. (This piece includes excerpts from the conversation which have been edited for length and clarity - you can hear the discussion in full above).
"Sunshine produces a hormone called serotonin", explains Freeman. "It makes us feel good, it makes us feel calm and focused and of course it helps us to produce vitamin D and nitric oxide to keep our body working well but, yes, it does have an impact on our brain and we don't fully understand what it does. Generally, it does make us feel more optimistic because things look good and we probably make decisions then because we think things are going to go well so that can influence how we behave."
Of course, it's not all good behaviourial changes. "One of the things that happens with sunshine is we all get out and interact so higher temperatures can cause arousal. In a study in Phoenix, Arizona, a researcher sat in a car at traffic lights. When the traffic light changed, they counted how many times people honked depending on the temperature from April to August in the same year. There's a linear relationship between the frequency and number of honks as the temperature gets up so people do get more aroused."
We also tend to spend a little more when the sun shines. "There is evidence that we spend a little bit more and we're probably not concentrating that well either", explains Freeman. "A study in Australia put funny objects around a shop and then asked people when they came out if they remember seeing them. People remembered three times more on cloudy days than on sunny days. When people are exposed to artificial sunlight and then tested to see what would they buy from a list, they tend to choose to buy more things and buy more unusual things."
Another area which sees a change when the sun shines is recruitment and, according to Freeman, clouds suit nerds. "There was a very interesting study about hiring people in different kinds of weather and the phrase from the researchers here was that clouds suit nerds. When interviewers in American colleges were looking at students on cloudy days, they were more likely to rate better students who had really strong records of academic performance.
You might think 'oh we want to eat less in the summer, it's hot', but in fact that's not true if you're a man
"On sunny days, they took into account people who had good athletic ability and good extracurricular activity. That's because our brain is so good at imagining how things fit in so we can see someone who's good at athletic performance on a sunny day."
Sunshine also affects our appetites and an important difference between men and women. "You might think 'oh we want to eat less in the summer, it's hot', but in fact that's not true if you're a man. Researchers looked at 3,000 participants and mapped their food over the whole year and saw that men were eating approximately 300 calories extra per day. That's quite a bit and it's enough to cause weight gain if you're doing it all the time.
"They then investigated what was going on behind this by exposing people to 25 minutes of sunlight and what they found was that this increased a hormone called ghrelin, a hormone that's boosts your appetite but only in men and this is fascinating. So if you're heading out in the sun to that BBQ, the sun might be causing you to eat a little bit more than you should. It's just a biological response to the sun."