Sunlight: what daylight does for your body

Sunlight is the energy source behind nearly every food chain on Earth.

Plants capture light and use it to make energy through photosynthesis. That energy moves through the food chain, which means much of the energy in the food you eat can ultimately be traced back to the sun.

But light also interacts with your body directly.

It helps your skin make vitamin D, tells your internal clock what time it is, influences sleep and alertness, and affects systems throughout your body.

What sunlight does for you

It helps your body make vitamin D. When ultraviolet B, or UVB, radiation reaches your skin, it begins a process that produces vitamin D.

Vitamin D helps your body absorb calcium and phosphorus, making it important for building and maintaining healthy bones. It also contributes to normal muscle and immune function.

Your vitamin D level is influenced by many things, including sun exposure, skin pigmentation, age, season, location, diet, and supplementation.

It sets your body clock. Your brain contains a master biological clock that helps coordinate daily rhythms throughout your body.

Specialized cells in your eyes detect light and send that information to the brain. Light in the morning and during the day tells your body that it is daytime, helping coordinate patterns of alertness, sleep, hormone release, body temperature, and other functions.

This is one reason getting outside after waking can be such a useful habit.

It supports sleep. Light and darkness help determine when your body feels awake and when it prepares for sleep.

Daytime light strengthens the signals that keep your circadian rhythm aligned. As evening arrives and light levels fall, your body begins preparing for nighttime, including increasing production of melatonin.

Getting enough light during the day and reducing bright light late at night can help reinforce that contrast.

It can influence your mood. Light exposure is closely connected with mood and mental health.

Seasonal affective disorder is a form of depression that follows a seasonal pattern, most commonly appearing during fall and winter when daylight hours become shorter. Bright light therapy is an established treatment for seasonal affective disorder.

Spending time outdoors also combines light exposure with other factors that can support wellbeing, including movement, time in nature, and changes in environment.

It helps regulate your daily temperature rhythm. Your core body temperature naturally changes throughout the day. It tends to rise during your active period and fall as your body prepares for sleep.

Light helps synchronize the circadian system that coordinates this rhythm.

It may affect your blood vessels. Research suggests that ultraviolet exposure can trigger the release of nitric oxide compounds stored in the skin. Nitric oxide helps blood vessels relax and may contribute to temporary reductions in blood pressure.

This is an interesting area of research, but it is not a reason to seek additional UV exposure. Regular physical activity, a balanced diet, adequate sleep, and appropriate medical care remain safer ways to support cardiovascular health.

Outdoor time supports children's eyes. Children who spend more time outdoors have a lower risk of developing myopia, or nearsightedness.

Researchers are still studying exactly why, but the much brighter light outdoors appears to play an important role. This benefit comes from being outdoors and does not require looking toward the sun.

Getting enough daylight

You do not need to chase a precise number of minutes to make daylight part of your routine.

Step outside during the day. Outdoor light is dramatically brighter than typical indoor lighting, even when the sky is cloudy.

Get some light earlier in your day. Morning light provides an important timing signal to your circadian system and can help reinforce a consistent sleep-wake schedule.

Count cloudy days. Clouds reduce brightness, but outdoor daylight is generally still much brighter than indoor light.

Let daylight into your home. Opening curtains and blinds can increase your exposure to natural light while you are indoors.

Protect your skin. More UV exposure is not always better. Avoid sunburn and follow appropriate sun-protection practices, particularly when the UV index is elevated or you will be outside for an extended period.

Remember that vitamin D does not have to come from the sun. Foods, fortified products, and supplements can also provide vitamin D. People who are concerned about their vitamin D levels can discuss testing and supplementation with a healthcare professional.

Sunlight is powerful, but one of its most useful benefits is also one of the simplest.

Step outside. Let your eyes experience the natural light around you without looking directly at the sun, and give your body a clear signal that the day has begun.