Summer is the UK’s best-loved season. It’s easy to see why, with the warmer, sunnier weather it brings. But the temperature isn’t the only reason people prefer midsummer to the dark days of winter. Many also report their mood is better during the warmer months.
But why is it that our mood changes so much through the seasons? While there are many complex reasons why the weather can have such a significant affect on our mood and wellbeing, the key answer lies in our brain – and the way almost all of our body’s systems are hardwired to respond to what’s going on around us.
Your body’s core temperature is set at 37°C. Temperature is regulated by an area of the brain known as the hypothalamus. This nerve centre receives information about temperature from all over the body and initiates actions to either cool down or warm up accordingly.
The outside temperature can also affect our biological clock – otherwise known as our circadian rhythms. These govern, among other functions, our sleep-wake cycles.
Our circadian rhythms are also regulated by the hypothalamus – more specifically, a part of it called the suprachiasmatic nucleus. The fact that both temperature control and sleep-wake cycles are governed from within the same region of the brain suggests they are inextricably connected.
This connection can also partly help to explain why our moods can shift so much from winter to summer. It’s the interaction between these nervous pathways that are believed to impact mood through their effect on sleep, mood-influencing neurotransmitters, and more.
For instance, in winter, many people find their mood takes a dip – especially during the long, dark days of midwinter. Some people even develop seasonal affective disorder (Sad), a condition associated with depressive episodes that fluctuate with the comings-and-goings of the different seasons – though it’s typically more common in the winter because of the darker days and cold temperatures.
Sad can also cause sleep disturbances, lethargy and appetite changes – particularly cravings for carbohydrates. As the summer months arrive, people with winter Sad usually find their symptoms significantly improve.
There’s some evidence that Sad is linked to secretion of a hormone called melatonin – a hormone that’s also linked to our circadian rhythms. Melatonin is produced by the pineal gland, which shares nervous connections with the hypothalamus and acts to control timing and quality of sleep.
Melatonin levels typically remain relatively low during the day – but levels start to creep up in the evening, reaching their highest levels in the middle of the night. But the lower levels of daylight in the winter can cause dysfunction with melatonin levels, typically increasing its secretion. This probably explains why people feel sleepier and more fatigued in winter – and which may in turn trigger depression.
But it’s not just melatonin that’s linked to Sad. Other neurotransmitters which act as mood boosters (such as serotonin) appear to be affected by dark and cold days too. There also seems to be a link with geographical location – with evidence showing the condition is more common in regions furthest from the equator, where there are extremes of daylight and temperature.
Summertime sadness
When summer finally makes an appearance, the effect of sunshine and heat upon the energy-boosting neurotransmitters (such as serotonin) makes a notable difference to mood. This may be partly due to increased amounts of vitamin D – which is made in the skin, and requires sunlight exposure to reach higher levels. Vitamin D has been proven to positively affect serotonin levels.
But not everyone finds themselves pleased by summer’s hotter temperatures and longer days. Some may find they feel more miserable this season.
There’s another variation of Sad, albeit rarer (affecting less than 10 per cent of Sad patients) that actually gets worse in summer.
It’s less clear why some people get Sad in the summertime – and is probably due to a range of factors. It may be due to the heat and humidity or even feelings of self-consciousness. It could possibly even be due to sleep disruptions – since the longer days might disrupt our circadian rhythm.
Certain health conditions may also influence how we cope with the warmer temperatures. Take the menopause, where symptoms such as hot flushes may be exacerbated by the warmer weather. Those dealing with these symptoms may find it becomes even more difficult during heat waves – and this may take a toll on their mental wellbeing.
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Some research does show that rising temperatures can be a precipitant for acute mental illness. One study examined a population of patients with bipolar disorder and found there was a significant peak in the number of hospital admissions in the summer months compared to patients with other psychiatric disorders. Their statistical analysis demonstrated that higher temperatures and solar radiation levels were the most significant determinants of acute episodes.
Another study has also suggested a link between increased temperatures and risk of suicidal behaviour.
The body’s natural responses to heat also feeds into the biological stress response. The mechanisms by which the body cools down, such as sweating and promoting blood flow to the skin, can cause dehydration and skin flushing. This may make people feel of frustrated and irritable, have trouble concentrating and may even impact the quality of sleep.
The interplay between temperature, sunlight, the body’s circadian clock and mood is a complex and intriguing conundrum – and one which is as unique as each person. While some of us are hard-wired to be sunchasers, others eagerly look forward to the dark days of winter. But in a world where climate change is a definite reality, we need to better understand how a warming world is going to affect our wellbeing.
Dan Baumgardt is a Senior Lecturer at the School of Physiology, Pharmacology and Neuroscience, University of Bristol
This article was originally published by The Conversation and is republished under a Creative Commons licence. Read the original article
