Sunlight contains ultraviolet (UV) rays that come in three different lengths: UV-A, UV-B, and UV-C.
UV-B rays are the ones that are capable of producing vitamin D in your body by acting on cholesterol found in your skin.
To make vitamin D, you need UV-B rays to come into direct contact with your skin. UV-B rays cannot penetrate glass, so you don’t make any vitamin D while you’re sitting in a car or by a window at work or at home.
But creating enough vitamin D in your body isn’t as simple as getting a certain number of minutes of sunlight exposure every day because the number and intensity of UV-B rays that reach your skin and lead to vitamin D production is affected by a number of different factors, the main ones being:
- Your Skin ColorLighter skin color allows deeper penetration by UV-B rays, which decreases the amount of sunlight exposure needed for adequate vitamin D production. If you have darker skin, it’s harder for UV-B rays to penetrate your skin and create vitamin D, which means that you need greater exposure to sunlight than someone with lighter skin.
- SeasonIf you live above 35 degrees latitude north or below 35 degrees latitude south, you receive little to no UV-B rays from some point in autumn to some point in spring. During this time, your body has to rely on the vitamin D that it has created during warmer months, or on intake of vitamin D through food and supplements.
- Altitude and LatitudeThe further north or south you live from the equator, the less exposure you have to UV-B rays.
The higher you live above sea level, the greater exposure you have to UV-B rays.
- Pollution and CloudsBoth decrease the number of UV-B rays that reach you.
- Your AgeWith each passing year, natural degenerative changes that occur in your skin make it harder for UV-B rays to convert cholesterol in your skin into vitamin D. It’s a known fact that elderly people need to rely more on food sources than sunlight for their vitamin D. At 70 years of age, the average person has approximately 30% of the capacity to generate vitamin D from sunlight that a 20-year old has.
Why is Vitamin D Important Again?
There’s a growing mountain of evidence that indicates that having enough vitamin D in your body is essential to reducing your risk of every disease that we know of. Every single one, no exaggeration.
In particular, vitamin D deficiency is strongly linked to increased risk of experiencing the following:
- Cancers of the breast, ovary, prostate, colon, esophagus, pancreas, and leukemia.A study published in the American Journal of Clinical Medicine in 2007 found that women who ingested 1,100 IUs of vitamin D and 1200 mg of calcium daily reduced their risk of developing cancer by 70%. 
- Diabetes types 1 and 2. [2,3]
- Osteoporosis. [4,5]
- Osteomalacia – chief complaint is typically generalized aches and pains throughout muscles and bones, often misdiagnosed as fibromyalgia or chronic fatigue syndrome. 
- Multiple sclerosis, rheumatoid arthritis, and other autoimmune illnesses. [7,8,9,10]
- Colds, flus, and other infectious diseases like tuberculosis.
- Rickets, which occurs at about six months of age in children who are vitamin D deficient. Presenting signs are typically skeletal deformities, growth retardation, and muscle weakness. 
How Much Vitamin D Do You Need for Your Best Health?
Based on all of the most recent research that I have reviewed on this matter, I feel that an optimal range is somewhere between 50 and 60 ng/ml (125 to 150 nmol/l). To convert ng/ml to nmol/l, simply multiply by 2.5.
Unfortunately, the only way to know where you’re at is to ask your doctor to include 25 (OH) D, also known as 25-hydroxy D, with your blood work during your next checkup. Some labs test for 1,25 hydroxy D, which isn’t as accurate a marker of your vitamin D status as 25 hydroxy D, so be sure to specifically ask for 25 hydroxy D.
You want your 25 hydroxy D level to be at least 30 ng/ml (75 nmol/l), but again, based on the research that I have reviewed, mainly that of Dr. Michael Holick, the optimal range appears to be 50 to 60 ng/ml. Some prominent physicians and vitamin D experts feel that one can go even higher, even up to 80 ng/ml. But my suggestion is to err on the side of caution and aim to be in the 50 to 60 range.
The 50 to 60 range is based on numerous studies that show strong relationships between these levels and reduced risk of a wide variety of chronic diseases and increased lifespan. This range is also based on the 25 hydroxy D levels of healthy people living in areas of the world (tropical and subtropical regions) where it’s quite common to receive more than enough sunlight exposure to ensure regular vitamin D production.
But here’s an important point that you want to keep in mind: When sunlight creates vitamin D in a healthy person and that person’s 25 hydroxy D is in the optimal range, that person is almost certainly benefiting from other natural compounds that are generated with sunlight exposure. Dr. Holick calls these other compounds “photo products,” and he and his team are currently researching the makeup and benefits of these photo products.
Put another way, establishing optimal vitamin D status mainly via healthy sunlight exposure may provide more health benefits than establishing optimal vitamin D status mainly via foods and supplements. Correct usage of foods and supplements only gives you the right amount of vitamin D – they don’t generate the photo products that sunlight does. As more information about these photo products becomes available, I’ll be sure to provide an update.
At the same time, it’s worth remembering that even responsible exposure to sunlight comes with some undesirable effects, like premature aging of skin and possibly increased risk of non-melanoma skin cancers, depending on your history of sunlight exposure.
So it’s too early to say which is more desirable between getting vitamin D mainly from sunlight vs. mainly from foods and supplements.
What we do know for sure is that keeping your 25 hydroxy D level somewhere between 50 and 60 ng/ml, possibly even up to 65 ng/ml can significantly decrease your risk of all types of disease and increase your lifespan. And a wise approach is likely getting vitamin D from a combination of responsible sunlight exposure and foods and supplements that come with vitamin D.
How Much Sun Should You Get?
It’s near impossible to provide specific recommendations in this area because of the many factors that affect your ability to generate vitamin D from sunlight. But we can provide general guidelines that should be helpful.
If you can’t pinpoint which of the four zones you live in, simply google “latitude of the name of your city.” Once you have the latitude of your city, you’ll know which of the four zones you live in:
- Tropics: 0 to 23 degrees (eg. Honolulu, HI: 21 degrees)
- Subtropics: 23 to 35 degrees (eg. Atlanta, GA: 33 degrees)
- Mid-Latitudes: 35 to 50 degrees (eg. Chicago, IL: 41 degrees)
- High Latitudes: 50 to 70 degrees (eg. Anchorage, AK: 61 degrees)
If you live in the tropics or subtropics, you have access to UV-B rays from the sun year-round, so it’s quite possible to get most or all of your vitamin D requirement from responsible exposure to sunlight, though recent studies indicate that a significant percentage of people living in Florida are vitamin D deficient because they just don’t get enough exposure to sunlight.
If you live in the mid-latitudes or high latitudes, you have little to no access to UV-B rays from some point in autumn to some point in spring. During these times, your body has to rely on its stores of vitamin D and/or vitamin D from foods and supplements.
It’s possible to live in the tropics and subtropics and not make enough vitamin D from sunlight alone.
And it’s possible to live in the mid-latitudes and high latitudes and have enough vitamin D in your system without eating vitamin D-rich foods and supplements throughout the winter if you generate sufficient reserves during warmer months.
The point is that if you live in the tropics or subtropics, you can likely get a good chunk of your vitamin D from sunlight, and if you live in the mid-latitudes or high latitudes, you can probably benefit from supplementation through diet.
Generally, here’s how to figure out how much sunlight exposure is ideal for your situation:
Estimate how long it would take your skin on any given day to turn a shade of pink from sunlight exposure. This is called a minimal erythemal dose, and it varies depending on a number of factors like time of day, time of year, your skin color, age, the latitude and altitude of your location, and how clear or cloudy the sky is.
Put another way (and this may be more helpful to people with darker skin color), your minimal erythemal dose is the amount of time that you need to feel like you just started to tan without coming close to getting burned. Your skin will feel like it has extra warmth to it.
Aim to expose your bare arms and legs to sunlight for about 25 to 50 percent of the amount of time that represents your minimal erythemal dose.
Clearly, this amount of time will vary from day to day and season to season. Dr. Michael Holick has tables in his book, The UV Advantage, that provides guidelines on how many minutes this would be for six different skin types at different times of the day and different months of the year for the four zones shown in the map above. If you want this type of guidance, it’s best to purchase his book for these tables.
If you prefer more of a natural and instinctive approach, you should just aim to get enough sunlight on your arms and legs to feel like you’re getting about halfway to the point where your skin will feel like it has gotten a healthy tan.
This is possible practically year-round for people living in the tropics and subtropics, and only possible from sometime in spring to sometime in autumn for people living in mid or high altitudes.
For days when you have to be under the sun for longer than about half of your minimal erythemal dose, once you get to this point, you can use protective clothing and hats, non-toxic sunscreen, or a combination of protective elements to ensure that you don’t get burned.
Do You Need to Take a Vitamin D Supplement?
The easiest way to figure this out is to have your blood tested for 25 hydroxy D. If you’re below 50 ng/ml, you can get more vitamin D through sunlight and/or take a vitamin D supplement.
If you live in the subtropics or tropics and you aren’t shy about getting sunlight exposure, chances are that you don’t need to take a vitamin D supplement, but again, the only way to be absolutely sure is to get a 25 hydroxy D test.
If you are indoors quite a lot, tend to stay out of the sun, and/or live in the mid or high latitudes, chances are good that you can benefit from vitamin D supplementation.
Here are some statistics, compiled by Dr. Holick earlier this decade, that illustrate how widespread vitamin D deficiency is in the United States:
- Seventy-six percent of pregnant women were found to be severely deficient in vitamin D.
- Eighty-one percent of babies born to women who were vitamin D deficient were deficient themselves, predisposing them to diabetes type 1, multiple sclerosis, schizophrenia, rickets, and a number of other diseases.
- Thirty-two percent of physicians and medical students were vitamin D deficient.
- Up to sixty percent of all hospital patients and eighty percent of nursing home residents are D deficient.
- Forty-two percent of African American women of childbearing age were D deficient.
- Close to fifty percent of girls between 9 and 11 years of age were vitamin D deficient.
Ask physicians who regularly check 25 hydroxy D levels in their patients, and I’m confident that they’ll agree that vitamin D is easily the most widespread nutritional deficiency in today’s population, especially among the middle and upper classes.
Getting back to supplementation, the first step is to consider including healthy foods that have naturally occurring vitamin D in your diet. Here are some food that are healthy choices for most people:
|Food Sources||Serving||Vitamin D (IU)|
|Wild salmon, canned||3 ounces||530|
|Cod liver oil||1 teaspoon||400|
|Sardines, canned||3 ounces||231|
|Organic egg yolk||1 medium||25|
Keep in mind that for every 100 IU that you ingest, you raise your 25 hydroxy D in ng/ml by about 1.
These days, I rarely encounter a person who can’t benefit from adding an additional 1,000 IU to their diet above and beyond what is obtained through sunlight exposure and eating the foods listed above.
Dr. Holick feels that every adult and child needs to take a minimum of 1,000 IU of vitamin D along with a multivitamin that contains 400 IU of vitamin D.
With the testing that I have done with clients over the years, I have found that the average person needs a minimum of 2,000 IU of D-3 daily.
I’ve even run into some clients who needed to increase their intake to 4,000 or 5,000 IUs, and in one case, 10,000 IUs per day to get their 25 hydroxy D into the optimal range – this last case was a woman who suffered with a severe deficiency (15 ng/ml) and symptoms of osteomalacia.
One last point for now: If you’re obese, you likely need to get more vitamin D than non-obese people, as obesity is a risk factor for vitamin D deficiency. The reason is that vitamin D gets trapped within fat tissue and can have some difficulty leaving to enter your bloodstream to supply the rest of your cells. Because of this, obese patients tend to need at least twice as much vitamin D as non-obese people in order to maintain optimal vitamin D status. 
I realize that all of the above is a good chunk of information to digest. I encourage you to take your time in considering all of this information and really invest some effort into making sure that your body has enough vitamin D year-round.
The science surrounding the human body’s need for vitamin D is groundbreaking in every way, and ensuring that you are getting enough is a guaranteed way of significantly improving the quality and length of your life.
It was impossible for me to include everything I wanted to in this post, so I’ll be writing shorter bits that explore different facets of vitamin D in the coming weeks. If you have any thoughts on this topic that you’d like to share, please use the “add new comment” featured below.
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