This is an important question to answer, because vitamin D from sun exposure is the best way to optimize your vitamin D levels and thereby reduce your risk of a wide range of diseases.
Unfortunately, it’s been suggested that only about 30 percent of Americans’ circulating vitamin D is the product of sunlight exposure, which is an unfortunate byproduct of public health agencies’ misguided advice to stay out of the sun to avoid cancer (when in fact vitamin D from sun exposure will prevent cancer). Another obvious reason is the majority of us work indoors, and when not working, do not spend enough time enjoying outdoor recreation.
Occasional sunlight exposure to your face and hands is insufficient for vitamin D nutrition for most people. To optimize your levels, you need to expose large portions of your skin to the sun, and you may need to do it for more than a few minutes. And, contrary to popular belief, the best time to be in the sun for vitamin D production is actually as near to solar noon as possible. Ultraviolet light from the sun comes in two main wavelengths — UVA and UVB. It’s important for you to understand the difference between them, and your risk factors from each.
First there is UVB, the healthy wavelengths that help your skin produce vitamin D. Then there is UVA, which is generally considered the unhealthy wavelengths because they penetrate your skin more deeply and cause more free radical damage. Not only that, but UVA rays are quite constant during ALL hours of daylight, throughout the entire year — unlike UVB, which are low in morning and evening, and high at midday.
So to use the sun to maximize your vitamin D production and minimize your risk of skin damage, the middle of the day (roughly between 10:00 a.m. and 2:00 p.m.) is the best and safest time. During this UVB-intense period you will need the shortest sun exposure time to produce the most vitamin D.
As far as the optimal length of exposure, you only need enough to have your skin turn the lightest shade of pink. This may only be a few minutes for those who have very pale skin.
Once you have reached this point your body will not make any additional vitamin D and any further exposure will only result in damage to your skin. Most people with fair skin will max out their vitamin D production in just 10-20 minutes, or, again, when their skin starts turning the lightest shade of pink. Some will need less, others more. The darker your skin, the longer exposure you will need to optimize your vitamin D production. If sun exposure is not an option a vitamin D3 supplement can be taken orally.
Research published by Grassroots Health from the D*Action study shows the average adult needs to take 8,000 IU’s of vitamin D per day in order to elevate their levels above 40 ng/ml, which they believe is the absolute minimum for disease prevention.
Important: Your Serum Level is what Really Matters
While 8,000 IU’s of vitamin D3 per day is a general recommendation that appears to be beneficial for most people, vitamin D experts from around the world are in agreement that the most important factor is your vitamin D serum level. There’s no specific dosage level at which “magic” happens. So the take-home message is that you need to take whatever dosage required to obtain a therapeutic level of vitamin D in your blood.
At the time (in 2007) the recommended level was 40-60 nanograms per milliliter (ng/ml). Since then, the optimal vitamin D level has been raised to 50-70 ng/ml, and when treating cancer or heart disease, as high as 70-100 ng/ml.