Vitamin D is known as the “sunshine vitamin” for good reason – after all, it’s the source of 90 percent of our daily vitamin D intake.

When exposed to the sun, your skin can manufacture its own vitamin D. “We each have vitamin D receptor cells that, through a chain of reactions starting with conversion of cholesterol in the skin, produce vitamin D3 when they’re exposed to ultraviolet B (UVB) from the sun,” says Yale Medicine dermatologist David J. Leffell, MD, chief of Dermatologic Surgery in an interview with Yale Medicine. Simply put, your body uses the sun’s rays to activate the production of vitamin D in the body.

HOW MUCH SUNLIGHT DO I NEED?

According to Cedric F. Garland, a medical professor at the University of California, San Diego, adequate vitamin D levels could be achieved by spending 15-30 minutes in the sun while it’s highest in the sky with 40 percent of your skin exposed. But on a second glance, these requirements are a bit trickier to achieve than they first appear.

While sunlight is an easy way to get your daily dose of vitamin D, it’s not nearly as simple as just stepping outside for a few minutes. Listed below are several physical and environmental factors that can impact how your body absorbs sunlight, complicating efforts to get the right amount of vitamin D you need to stay healthy.

SKIN PIGMENTATION

Your vitamin D intake can be influenced by the melanin in your skin, which reduces your body’s ability to make vitamin D when exposed to sunlight.

An article published in Environmental Health Perspectives pointed out the difference in vitamin D levels in average individuals with different skin pigmentations. If all individuals were exposed to sunlight during the summer for 30 minutes while wearing a bathing suit, the amount of vitamin D released in their bodies within the next 24 hours would be:

• White: 50,000 IU
• Tanned: 20,000 – 30,000 IU
• Dark-skinned: 8,000 – 10,000 IU

In contrast, the NIH recommends 400 – 800 IU for recommended daily intake, so sun exposure can be a great way to get more vitamin D.

What about sunscreen? While sunscreen can significantly reduce your body’s production of vitamin D in strict controlled conditions, normal usage doesn’t generally lead to vitamin D deficiency, according to an article in the British Journal of Dermatology.

LATITUDE

If you live closer to the equator in a country like Ecuador, you’re likely going to experience more direct sunlight than someone who lives near the Arctic Circle.

One study published in The Journal of the American Osteopathic Association found that latitude was a statistically significant risk factor for vitamin D deficiency, along with individuals with darker skin tones. Another study found that vitamin D3 production from sunlight was minimal in anyone north or south of the 33 degree latitude line during winter. In the U.S., that includes anyone north of U.S. cities like Los Angeles, Phoenix, Dallas, and Atlanta.

However, a study published in The Journal of Clinical Endocrinology & Metabolism found similar percentages of people with low vitamin D levels in southern Florida, a climate with year-round sunshine, as those in Boston, located in the northeastern U.S. Therefore, we can assume that levels of vitamin D exposure to sunshine is fairly consistent across the United States.

SEASONS

As the seasons change, so does the angle at which the sun is hitting our location on earth – which affects how much direct sunlight we’re exposed to. Seasons also change our clothing choices. You’ll likely get more vitamin D wearing a bathing suit in the summer than when you’re wrapped up in parkas, hats, and scarves during the cold winter months.

In cities as far north as Boston, research found that human skin did not produce any pre-vitamin D on cloudless days from November to February. Check out these 6 ways to get more vitamin D in your diet this winter!

TIME OF DAY

Are you heading outside during the early morning or the late evening? You’ll probably get less sunlight than if you head out on a walk during your lunch break. One 2013 study found that vitamin D production in the body was highest between 11 a.m. and 2 p.m. Just remember that you’ll need less time in the sun during these hours, and sunburn risk can increase during this time.

AIR POLLUTION

If you live in an area with poor air quality, you may not get as much vitamin D from sunlight as those who live in areas with better air quality. A study published in the The Journal of Clinical Endocrinology & Metabolism found that air pollution could be a risk factor for low vitamin D levels, and another study found that living in a polluted area can play a significant independent role in vitamin D deficiency.

According to research published in The Journal of Rural Health, residents of large metropolitan populations were 49 percent more likely to experience low vitamin D levels than those in urban areas. If you’re a resident of a big city, you may be at a higher risk for low vitamin D levels. Check out our blog to find out how you can get more vitamin D in your diet.

SUN SAFETY TIPS

With all these different factors surrounding sunlight, it’s important to consider your environment, risk factors, and personal characteristics that might influence how much vitamin D you’re getting from the sun. Regardless, here are a few practical tips from the CDC that you can apply to stay safe while you’re having fun in the sun:

• If you’re planning to be out in the sun for longer than 15 minutes, bring long-sleeve shirts, long pants, and a hat to protect your skin from too much sun exposure.
• Wear sunglasses that block UVA and UVB rays to protect your eyes.
• Wear sunscreen with SPF 15 or higher, and reapply every two hours or after swimming, sweating, or drying off.

Wondering if you need more vitamin D in your life? With an at-home vitamin D test from empowerDX, you can shed some light on your vitamin D levels and take steps towards becoming a healthier you.