Over many centuries of human history, the shift from a hunter-gatherer to an agricultural-based to an industrialized society also meant less vitamin D from sun exposure.
Ancient civilizations all developed in areas of the world that were subtropical in climate and that made living outdoors year-round a possibility. Until modern times, human beings have always spent a great deal of time outdoors. But as the human race migrated from subtropical to less temperate climates, this has changed dramatically.
Avoiding sun exposure has lead to widespread vitamin D deficiencies. Whenever tests are done to measure vitamin D levels in numerous subjects, the results show that the population as a whole is suffering from chronic vitamin D deficiency. A typical study, done in the Massachusetts General Hospital, found over 50% of inpatients had vitamin D deficiencies. These numbers are probably reflective of most of the population.
Today, many of us work indoors and use our cars to get from place to place, instead of walking. In addition to that, many people use sunscreen whenever they spend any time out in the sun.
What about the dangers of skin cancer from sun exposure? There’s no question that chronic, excessive exposure to sunlight increases risk of non-melanoma skin cancer. But there’s very little evidence that sensible, moderate sun exposure increases your risk of the most deadly form of skin cancer, melanoma. In fact, there’s good evidence to suggest that it may actually decrease your risk.
The best place to get vitamin D is from your skin being exposed to the UV-B rays that are in normal sunlight. Vitamin D from sunlight acts as a pro-hormone, which converts into 25-hydroxyvitamin D, or vitamin D3 in your body.
Ultraviolet-B Is What Generates Vitamin D in Your Skin. UV light is divided into three bands, or wavelength ranges, which are referred to as UVA, UVB and UVC. UVB is the primary cause of sunburn caused by overexposure to sunlight. However, UVB sunlight also produces vitamin D in your skin. The amount produced depends on exposure time, tome of day, geographic location, season, clouds, pollution, a person's age, the amount of skin surface exposed, and skin color.
A common misconception is that occasional exposure of your face and hands to sunlight is sufficient for vitamin D production. Actually, this exposure can provide 200-400 IU vitamin D during the summer months, but this is insufficient for optimal health.
Your body can only produce a limited amount of vitamin D every day. You can tell you’ve reached your optimal exposure for the day when your skin turns a very light shade of pink, within 20 minutes for light-skinned people. Dark complected people may need several times the amount for the same benefits. But after that, you’re only increasing your chances of getting sunburn, and sunburn has been clearly related to an increased risk of skin cancer.
Ultraviolet exposure beyond the minimal dose does not increase your vitamin D production any further.
Interestingly, if you avoid getting sunburned, yet have regular sun exposure, you'll have a decreased risk of melanoma. Optimizing your sun exposure in this way also reduces your risk of 16 other common cancers!
For most people living in the United States, two or three hours a week in the summer months, with half your skin area exposed, and no sunscreen, is ideal. The ironic thing is that the best time to get the maximum amount of vitamin D from sun exposure is in the middle of the day, exactly the time that you have been warned to avoid it.
Moderation is the key; you only want to stay out as long it takes for your skin to get slightly pink (if you're light-skinned), no more. This usually amounts to about a half hour on average for light skinned people.
Where you live makes a difference. The other primary factor to consider when you get your vitamin D from sun exposure is the distance you live from the equator. If you live north of the 30th parallel in the northern hemisphere, or south of the 30th parallel in the southern hemisphere, the sun is not strong enough for about half of the year to produce vitamin D from sun exposure. The further you go away from the equator, the shorter the vitamin D season gets.
To find the latitude where you live,try
this easy-to-use International Latitude/Longitude Finder
Fair-skinned individuals need far less exposure to produce vitamin D from sun light than darker races. Lighter skin allows for greater penetration of UV-B, leading to higher levels of vitamin D. People with pale skin will reach a point after about 20 minutes of mid-day exposure to UVB light when vitamin D will no longer be produced.
Dark-skinned individuals need considerably more sun to generate adequate vitamin D. This is one of the reasons why breast and prostate cancer rates are so much higher in dark-complected races who live in temperate climates.
A person with very deep skin pigmentation has natural sun protection that’s similar to a sunscreen with a SPF of 15-30. It can take 3-6 times longer (up to an hour or two) for darker-pigmented skin to reach the maximum production of vitamin D. However, skin pigmentation does not affect the amount of vitamin D that can be obtained through sun exposure.
Unless you practice regular sunbathing (2 or 3 hours a week), you're not getting enough vitamin D from sun exposure. You really can't get enough from your diet. If you don't compensate by using vitamin D supplements, you almost certainly have low vitamin D levels in your bloodstream.
The only way to determine this for sure is to get your vitamin D levels tested. You can arrange a vitamin D blood test with your health care provider, or order an inexpensive home blood test.
See Vitamin D Blood Test for more details.
Supplementing with vitamin D is easy — in the summer months, just spend a few hours each week sunbathing. Your skin produces more than 10,000 IU vitamin D with just 30 minutes summer sun exposure in a bathing suit (without sunscreen). In the winter months, take natural vitamin D supplements in the form of D-3 (cholocalcerifol).
If your blood levels of vitamin D are low to begin with, it can take a few months to raise your vitamin D levels using supplements; and then you'd have to guess whether you're taking enough. Most people tend to use too little, due to unwarranted fears of toxicity.
A safe way to do it is to take 5,000IU per day for three months, then get a 25-hydroxyvitamin D test to measure your blood levels. Adjust your dosage from there, so that your blood levels are optimal.
Recommended Dosages for Preventive Health. If you're not getting decent sun exposure, you should be taking at least 1,000-2,000IU as a minimum daily dose. 5,000IU per day is not unreasonable, especially if you live in northern latitudes, are dark-skinned or overweight.
See Vitamin D Dosage for more details.
Vitamin D may be the most important supplement you can take, according to Dr. Joseph Mercola, the internet's most popular alternative-health expert. Fortunately, vitamin D supplements are very inexpensive.
Other pages on this website about vitamin D:
Other Great Resources for Vitamin D Information:
Grassroots Health A consortium committed to solving the worldwide vitamin D deficiency epidemic.
Dr. Mercola Lecture on the most up-to-date science on vitamin D.
How Much Vitamin D Do You Need? An article by Dr. Mercola.
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