Summer days just seem good for the soul, don't they? The days are long and the sun shines bright. Depending on where in the world you are reading this, summer happens at different times, but no matter where you are it's hard not to love the time of the year.
As a functional medicine practitioner who primarily consults via webcam, I see this summer-loving phenomenon no matter where my patients live. So what is it about the warmer months? This is the science of summer.
1. Sunlight eases mild depression.
Shorter grey fall and winter days can lead SAD or seasonal affective disorder. In fact, about 6 percent of people have winter depression and up to 20 percent more have mild SAD. Four times more common in women, SAD is alleviated in the longer, sunnier days of summer. One mechanism for this is the brain's ability to produce more of your feel-good neurotransmitter serotonin with sunlight.
2. We tend to eat more fresh fruits and vegetables.
Another factor to consider is fresh produce. There's something ancestral about eating fresh, seasonal fruits and vegetables from local farms during the summer months. These foods are rich in vitamins and phytonutrients that boost your immune system, brain, and mood. If you feel better in the summer months, it may be as simple as an increase in foods from the farmers market.
3. The sun gives your brain a boost.
Good ol' vitamin D, the sunshine vitamin, is synthesized when you're outside in the sun. Vitamin D is super important—responsible for hundreds of different pathways that control your mood, immune system, and brain. Every single cell of your body needs vitamin D to function optimally, and summer it the ideal for time in the sun.
4. You spend more time in nature.
There's no denying that spending time in nature is healing to the mind and body. During the colder months, we tend to spend more of our days inside and disconnected with nature. One study, published in the Proceedings of the National Academy of Sciences shows just how remarkable nature is. The group of people who walked for 90 minutes in nature reported fewer negative thoughts compared to the group who walked in the city. Functional MRI brain scans also revealed less activity in the subgenual prefrontal cortex, an area of your brain that plays a role in mood disorders and negative thoughts in the nature group. Those who walked in the city showed none of these benefits. Sorry city folks.
5. You are stuck inside less often.
Since we are inside more during the chilly time of the year, this can be a breeding ground for viruses. In rooms with poorer ventilation, colds were more likely to thrive and the cold virus also tends to spread more during colder months. Other studies from the NIH found that the flu virus actually became tougher during winter.
6. You're probably getting better sleep.
When sunlight hits your eyes, a message is sent to your brain's pineal gland to slow down producing your sleepy-time hormone melatonin. As the sun goes down it signals your body to ramp up melatonin for you to get a good nights rest. During darker, winter days the sunlight can't shut off the melatonin mechanism as much during the day, leading to lower production at night, causing poorer sleep.
7. Your genes change with the seasons.
One fascinating study published in the scientific journal Nature, found that around 25 percent our DNA actually changes with the seasons! The study found that during the winter months, DNA changes were (presumably) occurring to prepare for the increase in viruses that spread more during the winter. In the summer, different sets of genes are more greatly expressed, specifically genes that govern blood sugar balance, which calms cravings and will help burn winter fat.
8. Your immune system is on fire (in a good way).
Sun exposure can help suppress an overactive immune system, which could explain why sunlight is used to treat autoimmune diseases like psoriasis. And since white blood cells—which play a key role in fighting diseases and defending the body against infection—increase with sun exposure, moderate amounts of time in the sun are very helpful for your immune system.
But how important is the weather to your happiness, health and mood?
After reading all my nerdy science reasons why we tend to overflow with awesomeness during the summer, you might assume then that people are happier when they are in warmer, sunnier places, right? Well, don't buy your one-way ticket to a tropical destination, just yet. One study found that people were no happier in southern California than in the cold, cloudy, snowy and rainy Midwest (gasp, I know it's hard to believe Los Angelenos). Even though the Midwesterners complained more about the weather, they were overall no less unhappy than the southern Californians.
Other studies point to the fact that while indeed suicide rates are higher in the Arctic circle, they are actually higher in warmer South Korea than in icy Scandinavian countries. Speaking of Scandinavians, they are listed as some of the happiest people in the world, despite their gloomy cold weather, comparatively. Must be all the hygge.
Another factor may be the genetics of different populations, such as genes that play a role in vitamin D metabolism. Seeing hundreds of patients with methylation gene impairments and people with VDR (vitamin D receptor cite) gene changes tend to have lower vitamin D levels and are more prone to mood disorders. Another thing to consider is the diet of very happy people who live in colder, cloudier parts of the world, as traditional diets consist of a lot of wild caught fatty fish—rich in vitamin D.
So does the weather play in a role in your mood, energy and health? Absolutely. But it's actually not nearly as important as what you eat, your social ties, your outlook on life, and your activity levels.