The UV index is a measure of the intensity of ultraviolet radiation B (UVB) from the sun. It is expressed as a number on a scale of 0-11. A higher number indicates a higher sunlight intensity. Exposure to the ultraviolet B (UVB) portion of sunlight is necessary to cause the skin to produce vitamin D. Nevertheless, unless the body is deeply tanned or naturally very dark, a very high UV index can cause sunburn, so caution is necessary.
A low UV index is also problematic.
However, if the UV index is very low, it cannot stimulate the production of vitamin D in the skin. Vitamin D production is essential for human health. Thus, lack of vitamin D may be a major reason that flu-like diseases occur primarily during winter, when there is little or no vitamin D production. This, of course varies according to latitude.
A List of vitamin D benefits from Business Insider.
A recent article from Business Insider (a Philippines online paper) discussed various health effects of vitamin D and sun exposure. Here are some of their salient points, not all of which are correct.
- The primary cause of vitamin D deficiency is sun deprivation (correct).
- Vitamin D helps keep the immune system, so deficiency could be the reason for frequent flu (correct).
- You can get more vitamin D by spending at least 5 to 10 minutes outside 3 times a week without sunscreen (correct).
How much vitamin D does a person need?
- The most incorrect statement of the article is this. The average adult needs around 600 international units (IU) of vitamin D a day (not correct). For reference, a serving of salmon contains roughly 400 IU (not correct). 20 minutes of full-body, unobstructed sunlight can cause the skin to produce up to 20,000 IU of vitamin D. If 600 IU were the only source of vitamin D, one would produce a level of six ng/ml, which would be woefully inadequate. 600 IU is only slightly better than nothing.
- Fifteen minutes of non-burning midday sun (without sunscreen) would optimize vitamin D levels in a few days. Dark-skinned individuals would need much more exposure, up to an hour.
Getting more frequent colds or respiratory infections could be a symptom of vitamin D deficiency (correct). However, it is even more likely to be a sign of sunlight deprivation.
- Colds and flu nearly disappear in the summer when the sun is direct. During this time of the coronavirus epidemic, everyone on earth needs daily direct or indirect sun exposure. Those who do not tan can obtain plenty of sunlight from being outdoors under an umbrella or even in the shade near where the sun is shining.
Bone diseases, vitamin D and sunlight.
- Vitamin D deficiency can cause Osteomalacia and Osteoporosis, conditions where your bones become less dense (correct). Sun exposure produces about 90% of the body’s serum levels of vitamin D. In addition, not all vitamin D supplement studies have produced stronger bones.
Sunlight is king for increasing bone strength.
- However, sun exposure, or exposure to sunbeds (tanning beds) produces marvelous results. For example, a Spanish study showed that women in Spain—those who regularly enjoyed sun exposure—had about one-eleventh the risk of hip fractures as women who had little exposure. Women who use sunbeds also have profoundly higher bone mass than women who do not use them. Their vitamin D levels are also remarkably higher.
Mental problems due to a low UV index and subsequent vitamin D deficiency.
- Vitamin D has some links to depression (correct). Nevertheless, that link in my opinion is 100% due to to sun deprivation. Dr. Gavin Lambert and his colleagues in Australia measured serotonin levels in response to varying degrees of bright light. To do so, they drew blood samples from the internal jugular veins of 101 men and compared the serotonin concentrations of the blood to weather conditions and seasons. The results were remarkable: Men measured on a very bright day produced eight times more serotonin than those measured on a cloudy, dismal day.
More on the UV index and “solar noon.”
When meteorologists report UV index, the emphasis usually warns against the maximum UV level. That level generally occurs around “solar noon.” Solar noon is a four-hour period stretching from 10:00 AM to 2:00 PM. As you have probably noticed, forecasters constantly warn us to avoid the 10:00 to 2:00 hours. Avoiding intense UV radiation is their watchword. Many of them say, “Get sun exposure in the early morning or late afternoon to produce vitamin D.” They should know that the UV index must be over 3 to produce vitamin D.
These reporters do not understand how low UV index hinders vitamin D production.
They do not comprehend that UV index is so weak in the morning that it produces absolutely no vitamin D. The same is true in the evening. Therefore, the closer to solar noon you plan your outdoor time, the more vitamin D you will produce. Vitamin D produced in the skin from solar UVB exposure does not lead to vitamin D toxicity and is safe, as the body limits its own production.
Another method to measure the efficacy of sunlight for vitamin D is to stand in the sun at any time of day and observe your shadow. If your shadow is shorter than your height, you are producing vitamin D. This, the shorter the shadow, better.
Caveats regarding the UV index and vitamin D. Morning sun is still very healthful.
Early morning sun exposure, when the UV index is very low, (under 3) has remarkable health effects. These include resetting the circadian rhythm, increasing production of serotonin, lowering blood pressure through nitric-oxide production and assisting weight loss. Nevertheless, vitamin D stimulation in the skin is not one of the health effects of early morning light.
So safely soak up the sun at any time of day and reap the health benefits. Never burn.
By Marc Sorenson, EdD Sunlight Institute…
Research from Singapore, a very sunny country, demonstrated that 57% of older adults with hip fractures were vitamin D deficient. The researchers note that in Western countries with seasonal winters, D deficiency is common due to the reduction in sunlight. But on measuring serum vitamin D in fracture patients in sunny Singapore, they found that 57.5% were suffering deficiency and 34.5% were suffering insufficiency. Only 8% of the patients had normal vitamin D levels.
One might ask why people residing in a sunny, predominantly tropical climate would have such a high degree of vitamin D deficiency and consequently high fracture risk. Further study found the answer: Most of the people who suffered fractures had been housebound and had little sun exposure. The authors of the paper made the following statement: “Another factor was Malay ethnicity (dark skin, which inhibits vitamin D production), and clothing habits that prevented sun exposure.”
The authors of the paper concluded with this statement: “Vitamin D deficiency and insufficiency are common in patients with hip fracture in Singapore. Vitamin D deficiency was associated with being housebound and those of Malay ethnicity. Clothing habits resulting in reduced sunlight exposure may increase the risk of vitamin D deficiency.”
The same pattern of high D deficiency also exists among youth in some sunny countries; in Qatar deficiency is common.  Sixty-eight percent of the children there are deficient and the girls are especially likely to be deficient. Low duration of time spent outdoors is a major predictor of deficiency, and the children who are deficient suffer a greater incidence of rickets, fractures, and gastroenteritis.
And finally, I would like to remind the readers of research from Spain that I have cited on various occasions. Women who spend their time indoors are about 11 times more likely to have a fracture as those who regularly seek the sun.
A major message is this: If the sunlight is all around you and you don’t expose yourself to it, it will do you no good. You may a well live in the Arctic Circle.
Carefully embrace the sun and save your bones.
 Ramason R, Selvaganapathi N, Ismail NH, Wong WC, Rajamoney GN, Chong MS. Prevalence of vitamin D deficiency in patients with hip fracture seen in an orthogeriatric service in sunny Singapore. Geriatr Orthop Surg Rehabil. 2014 Jun;5(2):82-6
 Bener A, Al-Ali M, Hoffmann GF. High prevalence of vitamin D deficiency in young children in a highly sunny humid country: a global health problem. Minerva Pediatr. 2009 Feb;61(1):15-22.
 Larrosa M, Casado E, Gómez A, Moreno M, Berlanga E, Ramón J, Gratacós J. Vitamin D deficiency and related factors in patients with osteoporotic hip fracture. Med Clin (BARC) 2008;130:6-9.
.Marc Sorenson, EdD, Sunlight Institute
While perusing the medical and scientific literature for research that would be pertinent for my upcoming book on the value of sunlight exposure, I found a most interesting paper on sunlight exposure and bone strength.[i] The researchers searched the literature on three groups of patients, Alzheimer’s, Parkinson’s and Stroke which correlated to very high fracture rates among patients suffering from those diseases. They then found three randomized, controlled studies that determined the efficacy of sunlight exposure for reducing the risk of hip fractures in patients with these diseases.
In each study, there was a control group that did not receive the exposure and an experimental group that received regular sunlight exposure to a small part of the body daily for a year. The results were impressive: For Alzheimer’s patients, the reduction in hip fractures was 78% compared to the controls who stayed inside; for Parkinson’s patients, 73%; for stroke patients, 83%. Overall, the risk of the hip fracture was reduced by 77% in the sunlight exposed groups. Bone mass also increased in each sunlight-exposed group, so osteoporosis was obviously reversed. Did you even realize that such a thing was possible? You probably knew it only if you have been reading the Sunlight Institute blogs. There is an even more impressive study that I always mention when writing about sunlight and osteoporosis. For example, an investigation from Spain in 2008 concluded that women who actively participated in sun exposure had one-eleventh the chance of a hip fracture as those who stayed indoors.[ii] It appears from the materials on the different disease groups mentioned above, that reversibility is a reality, but how much more important is it to prevent the disease in the first place? The women in Spain did exactly that.
The National Osteoporosis Foundation estimates that osteoporosis was responsible for more than 2 million fractures in 2005, including 297,000 hip fractures, 547,000 vertebral fractures, 397,000 wrist fractures, 135,000 pelvic fractures and 675,000 fractures at other sites. The foundation also estimates that the number of osteoporotic fractures is expected to rise to more than 3,000,000 by 2025, and that an average 24 % of hip-fracture patients aged 50 and over die within one year following the occurrence of their fracture.[iii] If we take 24% of just the hip fractures that cause death we see that osteoporosis kills at least 71,280 people per year. Larrosa, M. Vitamin D deficiency and related factors in patients with osteoporotic hip fracture. Med Clin (BARC) 2008;130:6-9.
Do you believe that it might be worth a daily sunbath to save the lives of 70,000 people per year? Do you believe that it would be worth daily exposure (unprotected by sunscreen) to the sun (when possible) to reduce your own risk of fracture? Then why don’t we know about these statistics and the marvelous prophylactic effects of sunlight? That answers are simple: (1) it doesn’t sell any Fosamax or Boniva. (2) It doesn’t sell any noxious, deadly sunscreens. (3) It would be unthinkable for most dermatologists to admit that soaking up a little sun each day might be good for us. It has been said, “And ye shall know the truth and the truth shall make you free.”[iv] Now you have boned up on bone strength and sunlight, and you know the truth.
My fervent hope is that all may be free from the deceptions of those who would ignore the truth in favor of making another dollar.
[i] Iwamoto J, Takeda T, Matsumoto H. Sunlight exposure is important for preventing hip fractures in patients with Alzheimer’s disease, Parkinson’s disease, or stroke. Acta Neurol Scand. 2012 Apr;125(4):279-84
[ii] Larrosa, M. Vitamin D deficiency and related factors in patients with osteoporotic hip fracture. Med Clin (BARC) 2008;130:6-9.
[iii] National Osteoporosis Foundation, Fast Facts on Osteoporosis. Accessed Nov. 20, 2009 at http://www.nof.org/osteoporosis/diseasefacts.htm
[iv] John 8:32 (KJV)