Vitamin D plays an essential role in many areas of your health. It contributes to bone strength, heart health, and disease prevention. It also plays a vital role in the immune system.

One study found that insufficient levels of vitamin D3 have been reported in 36 percent of healthy adolescents and 57 percent of adults in the U.S. Other studies estimate that one billion people worldwide have insufficient vitamin D3 levels.

A significant challenge to overcome high rates of vitamin D deficiency is that it’s not easy to maintain sufficient levels of vitamin D with diet and lifestyle, according to Amy Myers, M.D.

Nicknamed the “sunshine vitamin,” the primary source of vitamin D is through sun exposure, which triggers a process on your skin that produces vitamin D.

However, busy lifestyles mean we’re spending fewer hours outside. On top of that, fear of skin cancer means wearing sunscreen during that limited sun exposure, which reduces the body’s ability to absorb vitamin D by more than 90 percent. Living farther north, where you receive fewer direct sun rays, or having darker skin, which consumes less sunlight, further reduces your ability to produce vitamin D.

Not many foods are naturally rich in vitamin D. These foods include salmon, fish liver oil, organ meat, such as the beef liver and egg yolks.

Vitamin D works as a kind of light switch in your body, turning on or off genes and processes that your body needs to maintain health. Active vitamin D is sent to many different areas of your body, including your bones, intestines, colon, brain, and immune cells, which all have vitamin D receptors, according to Meyers. The active vitamin D binds to these receptors and promotes vitamin D responsive genes, essentially turning them on.

Adequate levels of Vitamin D reduce your risk of infectious disease by strengthening your natural immune system, according to Myers. Vitamin D turns on essential peptides in your immune system that trigger a strong anti-microbial response, allowing you to quickly and effectively fight off invaders before they can develop into a full-blown infection.

If you decide to take a vitamin D supplement, it should be vitamin D3, the form of the vitamin that is most beneficial to your body. Also, because vitamin D is fat-soluble, it should be taken with a meal for better absorption.

According to a report from WebMD, one study proved that people who take their vitamin D supplement with the most substantial meal of the day get as much as 50 percent better absorption.