If you're heard or read about the advantages of making vitamin D from the sun, you may be ready to grab your towel and head to the nearest pool or beach for a few hours of sun worship. Not so fast. Chances are that you need to spend less than 30 minutes in the sun to give your body enough time to generate the vitamin D you need.
There are many different factors you need to consider when you’re trying to maximize your body’s vitamin D production. These considerations include the time of year, your geographic location, altitude, the time of day, and your skin type.
Determining your skin type
The type of skin you have determines how fast you reach a minimal erythemal dose and whether you can produce vitamin D sufficiently.
The threshold dose of sun that may produce sunburn is known as the minimal erythemal dose, or MED. If sun exposure continues longer than the MED, a sunburn occurs, with the possibility of long-term damage to your skin.
Dr. Thomas Fitzpatrick at Harvard Medical School created this categorization of skin types in 1975:
Type 1 skin is extremely fair, pale white skin. Eye color is usually blue or hazel, and hair color is often red or blond. These types have numerous freckles; they never tan, but just burn. These people have the highest risk of skin cancer. The group includes true redheads and albinos.
Type 2 skin is fair, and eye color is blue. These people may tan a little but usually burn. This group includes Northern Europeans and some Scandinavians. Hair color is usually brown although blond hair isn’t uncommon.
Type 3 skin is a darker shade of white. These people are sensitive to the sun and burn sometimes. They can tan to a light brown. This group includes darker Caucasians. Hair color is brown, as is eye color.
Type 4 skin is a light brown. It doesn’t burn easily, but instead tans to a medium brown. This group is the largest and includes American Indians, Hispanics, Mediterraneans, and Asians. These people have brown or black hair and brown eyes.
Type 5 skin usually isn’t sensitive to the sun. This type doesn’t burn easily, but instead tans to a medium or dark brown. This group also contains Hispanics, Middle Easterners, and some African Americans. They have black hair and brown eyes.
Type 6 skin isn’t sensitive to sun and rarely burns. Pigmentation is very dark. This group includes African Americans and dark-skinned Asians. These people have the lowest risk of skin cancer. Their hair is black and eyes are brown.
Clearly, as the darkness of your skin increases, the MED gets longer. Whereas in Chicago someone with type 1 skin requires just 16 minutes of midday sun to burn in mid-June, a person with type 6 skin requires 84 minutes. But this also means that the darker your skin pigment, the longer it takes to make a given amount of vitamin D.
Getting the right amount of sun for vitamin D
Ola Engelsen, a scientist at the Norwegian Institute for Air Research, has developed an online tool to allow you to calculate how much time you need in the sun to get any dose of vitamin D3. This calculator lets you enter all the factors that could influence your UVB exposure.
These factors include the following:
Latitude
Day of the year
Time of day
Skin type
Ground surface type
Altitude
The table shows vitamin D and MED values for people with different skin types in Indianapolis, Indiana, at midday on June 22 and December 22. These calculations are for someone at 39.5 degrees N latitude (Indianapolis, Indiana) on a clear day, wearing shorts and a T-shirt (25 percent skin exposure).
| Skin Type | Time to 1,000 IU (on June 22) | Time to MED (Produce a Sunburn) | Time to 1,000 IU (on December 22) |
|---|---|---|---|
| 1 | 4 min | 16 min | 37 min |
| 2 | 4 min | 20 min | 46 min |
| 3 | 5 min | 25 min | 55 min |
| 4 | 8 min | 37 min | 1 hr, 24 min |
| 5 | 11 min | 50 min | 1 hr, 55 min |
| 6 | 19 min | 84 min | 3 hr, 39 min |
When you’ve gotten the right amount of sun exposure, you need to put on sunscreen and protect your skin from damage.