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As long summer days and bright blue skies return, we feel a lift in our spirits as we flock to the beach or head out for summer walks. But why does a sunny day lift our spirits so much compared to a gray winter’s day?
For a start, all life on Earth is fueled by light from the Sun, except maybe deep in the ocean. Plants use the energy for photosynthesis, and growth, then are eaten by animals and so on up the chain.
Humans are diurnal creatures, meaning we are biologically programmed to be outside when the sun is shining and asleep inside at night. This is governed by our circadian cycle, which has evolved to match the 24-hour cycle of night and day.
This cycle is activated by sunlight and darkness. When sunlight hits our eyes, specialised cells in our retina respond to them and send signals to the “master clock” in our brain called the suprachiasmatic nucleus (SCN).
The same cells also signal areas that regulate mood and stress, triggering the release of serotonin, a neurotransmitter linked to calmness, focus and positive mood. As serotonin is a precursor for the production of melatonin, the hormone that signals the sleep cycle, this boost from sunlight helps sets us up for a healthy night-time sleep later.
As it grows dark, the pineal gland produces melatonin, which signals the body that it is time to sleep.
As serotonin is a precursor for the production of melatonin, the boost from sunlight helps set us up for a healthy night-time sleep later.
Our retinal cells are most sensitive to “blue light” so nowadays, when many people spend more time inside, or in front of screens late, which emit blue light, late into the night, this disrupts our circadian rhythms and sleep patterns.
As days get warmer and sunnier, it’s time to boost those serotonin levels with a morning walk, then switch off those devices and dimming lights in the evening to get your sleep cycles into sync with your natural circadian cycles.
With our modern-day penchant for indoor activity and staying up well past our bedtimes, nocturnal melatonin production is often below what it should be.
According to sleep researchers, as the light we get from being outside on a summer day can be a thousand times brighter than we’re ever likely to experience indoors , it’s important that people who work indoors get outside periodically, and moreover that we all try to sleep in dark rooms. This can have a major impact on melatonin rhythms and can result in improvements in mood, energy, and sleep quality.
For people in jobs in which sunlight exposure is limited, full-spectrum lighting may be helpful. Sunglasses may further limit the eyes’ access to full sunlight, thereby altering melatonin rhythms. Going shades-free in the daylight, even for just 10-15 minutes, could confer significant health benefits.
The UV from sunlight also produces vitamin D3 in our skin, which is converted into a usable form by our body.
Vitamin D is widely used by our bodies and is important for bone development
We need about 10 to 30 minutes of sun exposure a few times a week, depending on where we live, the amount of pigmentation in our skin, age and sunscreen use.
While often lumped in with other nutrients, vitamin D is more accurately described as a hormone – a potent chemical messenger shaped by sunlight and deeply embedded in how our bodies function. Synthesized when ultraviolet B rays from the sun strike the skin, vitamin D plays a critical backstage role in keeping us resilient, strong, and stable – both physically and mentally.
Vitamin D’s most well-known job is helping the body absorb calcium, a mineral essential for building and maintaining bones. Without it, even a calcium-rich diet can fall short. In children, deficiency can lead to soft, deformed bones (rickets), while adults may suffer from bone weakening and brittleness (osteomalacia and osteoporosis). In this sense, vitamin D acts as the gatekeeper of skeletal integrity, ensuring calcium gets where it’s needed.
Beyond bones, vitamin D is a major player in immune health. It helps the body recognise and fight off microbial invaders, from cold viruses to more serious infections. At the same time, it tempers the immune response, preventing it from going into overdrive and attacking the body itself – a balancing act that may help explain its link to lower risks of autoimmune diseases like multiple sclerosis and type 1 diabetes.
Researchers have discovered vitamin D receptors scattered throughout the brain, especially in regions that regulate emotion and behaviour. Low levels of vitamin D have been linked to mood disorders, including depression and seasonal affective disorder (SAD). Some evidence suggests it may help fine-tune levels of serotonin – a neurotransmitter known for influencing mood, sleep, and even appetite.
Vitamin D also enhances muscle strength, reducing the risk of falls in older adults. Its presence in muscle tissue suggests it helps maintain coordination and performance. It may even play a quiet role in cardiovascular health, with studies linking deficiency to high blood pressure and increased risk of heart disease, although these connections remain under investigation.
At the cellular level, vitamin D helps regulate cell growth and repair, with some evidence suggesting it may slow the progression of certain cancers. While this field is still emerging, vitamin D’s influence on gene expression and inflammation points to a broader role in preventing abnormal cell activity.
It doesn’t take much to get our vitamin D needs fulfilled – only about 10 to 30 minutes of sun exposure a few times a week, depending on where we live, the amount of pigmentation in our skin, age and sunscreen use.
