Vitamin D From Sun Exposure-Vitamin D is dubbed the “sunshine vitamin,” an appropriate name since the number one source of vitamin D is exposure to sunlight. It’s not as if the sun’s rays actually contain vitamin D. Instead, a substance called dehydrocholesterol each of us has on the surface of our skin is converted by sunlight to a vitamin D precursor. Once your skin makes the precursor, it’s modified by enzymes in your liver and kidneys to the active form of vitamin D called 1,25-dihydroxy vitamin D. So, you get vitamin D via a rather round-about path that begins with exposure to sunlight.
With exposure to sunlight being such an important source for making vitamin D, you might wonder if you’re getting enough sunlight to meet your body’s requirement for the sunshine vitamin. Many people are not. Is getting more sunlight the answer?
Can You Get Enough Vitamin D from Sun Exposure?
Unless you live in an area that gets direct sunlight year-round, like Hawaii, Arizona, Florida or Southern California, you’ll have a hard time meeting your body’s vitamin D needs through sun exposure alone. In addition, there are variables that affect how much vitamin D your body makes when you expose your skin to the sun. The time of day, time of year, latitude where you live, skin color, age, and even your body weight are all factors. Skin pigmentation is a major one. If you have darkly pigmented skin, you need up to 5 times the sun exposure to get adequate vitamin D that a person with fair skin does.
Even having a suntan increases the time you need to spend in the sun to get enough vitamin D. If you have fair skin and are young and healthy, you need as little as five minutes each day to get enough but as long as 20 or 30 minutes if you have very dark skin. As you might expect, wearing a sunscreen blocks the majority of UVB rays that boost vitamin D production.
Most people get enough vitamin D from sun exposure to avoid the deficiency disease called rickets but not enough to keep their vitamin D in the optimal range. One reason is that sunscreen use is so pervasive. One study showed that 40% of people who live in Southern Florida have low levels of vitamin D in the winter due to sunscreen use. However, not wearing sunscreen places you at risk of skin cancers and premature skin aging. So, it’s a delicate balancing act.
What about Dietary Vitamin D Sources?
If you don’t spend enough time in the sun, can you make up for the shortfall through diet? It’s challenging to get enough vitamin D through diet alone. Fatty fish is one of the few natural food sources of vitamin D. To make up for the shortfall, some packaged foods contain added vitamin D, including breakfast cereals, infant formulas, yogurt, milk, and orange juice. The form of vitamin D in these products is synthetic vitamin D2 whereas the form you find in fatty fish and your body makes from sun exposure is vitamin D3.
How Much Vitamin D Do You Need?
Although recommendations are that adults get between 600 IU and 800 IU of vitamin D daily (Institute of Medicine) most experts believe this is too low and should be more in the range of 1,000 IU to 2,000 IU. How hard is it to get that amount? First, let’s look at food. If you eat a piece of salmon, you’ll get around 500 IU. One-half cup of fortified cow’s milk will give you around 62 IU. An egg? About 140 IU. A cup of fortified yogurt, around 80 IU. You can see how hard it would be to meet your vitamin D needs through diet alone.
Now, let’s look at sun exposure. First, sunlight is made up of UVA and UVB rays. Only UVB rays boost vitamin D synthesis. These are the same rays that cause sunburn. In contrast, UVA rays penetrate more deeply and cause premature skin aging. Since UVB, but not UVA rays, are blocked by glass, you won’t get vitamin D exposure driving in your car unless you have an arm out the window as you drive. You also won’t get much exposure on a cloudy day, even if you walk around outside since the clouds absorb UVB rays. If you live in a city, pollution also limits the ability of UVB rays to reach your skin.
The angle of the sun is another factor that impacts UVB absorption and, therefore, vitamin D production. The closer the sun is to being directly above your head, the more UVB you’ll absorb. To get significant absorption, the angle should be no lower than 50 degrees. 90 degrees corresponds to directly overhead. Then there’s the issue of latitude. As you move north, the angle of the sun is lower at midday during the winter. So, living too far north reduces sun exposure, especially during the winter. In some parts of the country, like Alaska, only two months of the year provide enough UVB rays from the sun to make vitamin D.
Combine all of this with the fact that darker skin, obesity, and aging increases the amount of sun exposure you need to produce enough vitamin D, you see why it’s so challenging to get vitamin D from sun exposure alone. As you can see, it’s hard to make up the difference through diet.
The Bottom Line
It’s possible to get enough vitamin D from sun exposure but it’s not always practical unless you live in an area that gets direct sunlight most of the year, you’re a normal body weight, and have lighter colored skin. That’s why up to 70% of the population has a vitamin D level that’s either frankly deficient or sub-optimal. A better approach is to get your vitamin D level checked by your physician and take a supplement if you level is too low. Vitamin D plays too critical of a role in health to let yourself be deficient. Make sure you know what your vitamin D status is.
References:
National Institute of Health. “Vitamin D”
SunSafeRx. “Vitamin D And Sunlight: How To Know If Your Sun Exposure Is Producing Vitamin D”
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