Gauging UV Light Exposure to Reduce Vitamin D Deficiency


Vitamin D is widely recognized as a critical component to human health. The breadth of its importance is well-documented by Michael F. Holick, PhD, MD,1 a leading expert in vitamin D research, who wrote in the consumer press that if he could name one single “secret ingredient” to prevent and in many cases treat ailments including: heart disease, common cancers, stroke, types 1 and 2 diabetes, dementia, depression, insomnia, muscle weakness, joint pain, osteoporosis, psoriasis and hypertension, among others, it would be vitamin D. Holick’s findings are profound and encapsulated in his simple statement: “With adequate levels of vitamin D, you will live longer.” Table 1 summarizes some of the benefits of vitamin D he has found.

Considerable debate exists in the scientific community as to the minimum level of vitamin D necessary to optimize human health. The US Department of Agriculture’s (USDA’s) daily recommendation for vitamin D was increased from 400 to 600 IUs (international units) late in 2011.2 This amount is challenged by Holick and other health professionals who recommend a minimum of 1,000 IUs daily.3 In fact, according to a recent study in the Archives of Internal Medicine, 75% of Americans do not get enough vitamin D.4

Although vitamin D is generally referred to as a vitamin, it is actually the metabolic product 1,23-dihydroxyvitamin D, which is a secosteroid hormone found in the human body. For the purposes of this article, the more general term vitamin D will be used.5 There are three sources of vitamin D, including diet, supplements and ultraviolet (UV) light. Dietary sources for vitamin D are principally limited to oily fish, some mushrooms and fortified foods like milk, orange juice, yogurt and some cereals and cheeses. However, a diet full of these items is inadequate. According to Holick, to eat a sufficient amount of vitamin D— i.e., 1,000 to 2,000 IUs, one would need to consume either three cans of sardines, drink 10–20 glasses of fortified milk, gulp down 10–20 bowls of fortified cereal, snack on 50–100 egg yolks, or eat seven ounces of wild salmon for dinner every night.6

Supplements, a second source for vitamin D, present other challenges. Their effectiveness differs from person to person because individuals absorb supplements differently. If the level is too high, heart-related issues could appear, such as the risk of newly developed atrial fibrillation, which increases nearly threefold.7 Further, increasing one’s multiple vitamin intake can lead to dangerous levels of other vitamins; even with vitamin D supplements taken in high amounts alone there is a remote possibility of overdose,8 which can cause nausea, vomiting, loss of appetite, constipation, weight loss and depression. Also, calcium levels can be elevated by an overdose of vitamin D, which can cause calcification of the kidneys and major arteries, kidney failure and mental confusion.9 Lastly, vitamin D attained systemically does not remain in the system as long as it does when attained by the third source—i.e., exposure to natural light.10

The best source of vitamin D is from natural UVB light; high IU levels can be synthesized by the body relatively quickly, and the vitamin D produced lasts twice as long as other sources.11 More importantly, it is not possible to overdose on vitamin D produced via UV light exposure.

However, conversely to the benefits of attaining vitamin D from the sun, the damaging effects of excessive sun exposure are also well-documented. According to the Skin Cancer Foundation, about 90% of non-melanoma skin cancers and 65% of melanoma cases can be attributed to UV radiation from the sun. And just one or more blistering sunburns occurring in childhood or adolescence more than doubles the chance of developing melanoma later in life. Similarly, the risk for melanoma doubles if a person has had more than five sunburns at any age,12 and excessive UV radiation is also responsible for other skin problems such as wrinkling and blemishes.

So just as too much sun is harmful, too little is detrimental and the avoidance of sun exposure directly correlates to vitamin D deficiency; a recent study found that Caucasians who avoided sun exposure by wearing clothing or staying in the shade were twice as likely to suffer from vitamin D deficiency.13 Sunscreens also absorb or reflect UVB and negate the generation of the vitamin through the skin. Even low protection sunscreens of SPF 8 and SPF 15 have been found to block 87% and 93% of UVB, respectively.14 Since the UVB spectrum is responsible for facilitating vitamin D production, sunscreens with moderate to high SPF protection are detrimental to the body’s processing of this important nutrient. Conclusively, a carefully determined amount of exposure to UV light is necessary to optimize human health.

Vitamin D vs. Sunburn

Sayre and Dowdy concluded the safest way to obtain a sufficient dose of vitamin D is to be exposed to intense midday sun, since this is the peak period for the optimal identified UVB spectrum—i.e., 290 nm to 320 nm, which is responsible for vitamin D production. However, this short wavelength UVB is the same energy that produces sunburn, so midday is the key time of day to both optimize vitamin D production and cause skin damage. Importantly, however, Sayre and Dowdy also determined that a sufficient dose of vitamin D can be generated before sunburn damage from excessive UV exposure occurs.15

Multiple studies have concluded that sun exposure is the best means to obtain vitamin D but because no methods existed to judge how much exposure was adequate or safe, researchers broadly recommended supplementation. One such study16 found that UVB accounts for the majority of vitamin D production in humans, although no recommendation for exposure could be made that would be both safe and accurate for consumer use. Another study17 also determined sunlight to be an excellent means to obtain vitamin D; however, the researchers observed that individuals could not adequately judge how much exposure was necessary, so the side effects of too much UV made oral supplementation a safer choice.

An accurate gauge of UV exposure to produce optimum levels of vitamin D before sunburn results would therefore remove the dependency on supplements yet avoid the damage caused by sunburn. So how much UVB exposure allows for optimum vitamin D production? Holick calculated18 this amount by correlating the vitamin D generated by subjects clothed in bathing suits who were exposed to 1.0 minimum erythemal dose (MED) and determined that 20,000 to 50,000 IU of vitamin D was produced. MED is recognized in the sun care industry as the minimum amount of UV energy required to produce a minimum sunburn on average Fitzpatrick Type II skin.19 By cutting this exposure to a safer 0.5 MED and reducing the skin surface exposure to 25%, it can be assumed that the subjects would therefore generate a more moderate amount of vitamin D while wearing more clothing. The surface area of the human legs and arms is, on average, approximately 54% of the body.9 Also, short sleeves and pant legs cover as much as half of exposed skin, so 25% is a convenient and conservative exposure amount when considering common attire.

The estimated amount of vitamin D production was calculated by dividing the MED in half to 0.5—and consequently, the related vitamin D production in half, i.e., 10,000–25,000 IU— then further reducing the skin exposure to a more convenient 25%, resulting in 2,500–6,250 IU of vitamin D.

Thus 2,000–4,000 IU is a conservative approximation of the amount of vitamin D produced from 0.5 MED, depending on an individual’s ability to produce it. So with one exposure session managed by a UV sensor gauged at a 0.5 MED level,10 enough vitamin D would be generated.20 Consequently, individuals of a common Caucasian skin type exposing 25% of skin can maximize vitamin D production in half the time it would take for their skin to burn.

Gauging UV

Considering this small window of opportunity in which to optimize vitamin D production, a sensor was developed to indicate to consumers when enough UV light has been attained to stimulate a full dose of vitamin D production. Initially, a photosensitive material21 was identified, the substrate of which changes color based on the total amount of UV energy received. Changing from yellow-orange to red, it can be adjusted to various MED amounts; the described substrate material was manufactured to reach endpoint colors at different UV exposures, ranging from 0.6 to 3.0 MED. It should be noted that previous ink-based, color-change developments have been developed but they focus on the potential for sunburn rather than gauging vitamin D production as a result of UV exposure.

An independent study was conducted to verifya that the sensor’s color change was triggered by the same range in the UVB spectrum as is responsible for vitamin D production. Under natural sunlight, the sensor’s color change was measured by rating the dark red and light yellow color values as they changed with increased UV exposure time. The MED was established by a radiometerb coupled with a UVB detector, and a chromameterc compared the saturation levels of red and yellow within the material at each 0.1 MED value. As a clear indication of efficacy, red color saturations increased with each MED level, verifying the darkening of the substrate material. In addition, the yellow chromaticity fell with cumulative exposure, showing the reduction of the lighter (yellow) field of color. In the case of each color, the change in saturation paralleled the increase in MED. The authors concluded that the visual representation of the sensor would provide consumers with an accurate gauge of gradual UVB light exposure. Figure 1 shows the outdoor study results.

In addition, solar simulatorsd found the material to attain a full color conversion at 0.5 MED. Gradually higher irradiation doses showed increased darkening until reaching the endpoint of 0.5 MED. Rated 1 to 4 in color darkness, the visual observation matched the results of the outdoor study. Figure 2 shows the solar simulator results.

Also important to note is the fact that while both UVA and UVB radiation levels rise during midday, the increase in UVB is more dramatic.22 Since UVB is responsible for vitamin D production, the midday period is the optimal time to generate vitamin D. Longer exposure times to generate this same 2,000–4,000 IU of vitamin D are therefore necessary before and after midday.

Practical Application: Consumer Use

To ensure ease of use by the consumer, the photosensitive material was placed on a self-adhesive backing and die-cut into small, postage-stamp sized sensors. To use the sensor, consumers peel off the backing and place it either on clothing or skin and expose it to direct sunlight. A sun design in the corner of the sensor is printed in a dark red that exactly matches the color of the fully changed substrate. This color change establishes the end point of the gauged UV exposure time so that in effect, the sun design disappears when the user has attained enough UV light to stimulate the production of a full dose of vitamin D, at which point the sensor is discarded and sunscreen should be applied.

Instructions are included on the package and optimization guide insert to explain to consumers that 25% of skin must be exposed in order to achieve a full dose of vitamin D. The guide also explains that arms and legs are the recommended exposure areas. Unprotected exposure to the face should be avoided due to the detrimental effects the sun causes to this delicate skin. Further, the description of skin types as well as the sun’s intensity by geographic location, season and time of day are detailed because if misunderstood, the user may misinterpret the reading or think the sensor is malfunctioning. For instance, in northern climates or at the wrong time of day, the sun may not offer adequate intensity to allow for full vitamin D production, so the sensor would not properly change color.

Since too much UV light is damaging to the skin, it is important to educate consumers on the importance of following sensor use with immediate protection from additional exposure. Therefore, consumers are instructed to immediately apply sunscreen or to take cover from the sun once the sensor has fully changed color. For this reason, a sunscreen is often packaged with the sensor and this two-step process is clearly defined to avoid consumer confusion. Further, to allow for some error in consumer behavior, the calculations for the amount of skin exposure necessary to generate sufficient vitamin D are conservative.

Finally, UV light can cause color change if the sensor is not protected with special packaging. To prevent this, the sensors are sealed in foil envelopes to avoid light exposure before use. The envelopes also help to moderate the temperature of the substrate, as sensors should remain sealed and stored at room temperature until they are used.

Future Developments

Sensors gauged at different MED levels are being contemplated to accommodate various skin types. Lighter and darker complexions generate vitamin D with shorter or longer exposures, respectively, so a range of sensors that reach color endpoints faster or slower would match a broader population. Although Type II is the most prominent Caucasian skin type, for which this initial sensor is gauged, providing multiple sensors would be a natural extension to the current offering.


The process of attaining full UV exposure for vitamin D production, then stopping its potential to damage skin via the application of sunscreen complements work by sun care formulators in that it facilitates a regimen approach to sun exposure. Sunscreen use would be expected to increase with raised awareness and this more conscious method.

The best source of vitamin D is that produced by exposure to natural UVB light. Here, the author has described a sensor based on a photosensitive material that reacts via color-change to the proper UV light spectrum to indicate to the user when optimum vitamin D production has been achieved before sunburn occurs. This sensor-based indicator addresses one of the most serious health epidemics of modern times23 and provides a balanced approach for the user to determine adequate sun exposure time to attain this critical nutrient while avoiding too much sun and risking skin damage. The sensor answers the question: “How much sun is enough, but not too much?”

As a measure of UV light relative to vitamin D production, this sensor provides an alternative to solutions offered by health-related industries attempting to compensate for the vitamin D deficiency—specifically vitamin supplements and fortified foods. Importantly, it provides a renewed public awareness that natural sunshine is an important source of this vitamin.


  1. MF Holick, The Vitamin D Solution, Hudson Street Press, NY (Apr 2010)
  2. Institute of Medicine of the National Academies, DRIs for calcium and vitamin D, available at (Accessed Dec 27, 2011)
  3. Ibid Ref 1, pp 149
  4. University of Missouri-Columbia Archives of Internal Medicine, Vitamin D deficiency related to increased inflammation in healthy women, ScienceDaily (Apr 8, 2009)
  5. Ibid Ref 1, pp 13–14
  6. Ibid Ref 1, pp 23
  7. L Carroll, Vitamin D warning: Too much can harm your heart, available at (Accessed Dec 29, 2011)
  8. Ibid Ref 1, pp 214–216
  9. EJJ Cannell, The Vitamin D Council, Vitamin D toxicity, available at (Accessed Dec 27, 2011)
  10. Ibid Ref 1, pp 160
  11. Ibid Ref 1, pp 157–159
  12. ED Polsky, The Skin Cancer Foundation, Skin cancer facts, available at (Accessed Dec 27, 2011)
  13. M Brandt, Avoiding sun exposure may lead to vitamin D deficiency in Caucasians, Stanford School of Medicine, available at: (Accessed Dec 29, 2011)
  14. V Iannelli, Pediatrics, SPF—Sun protection factor and sunscreen, available at (Accessed Dec 29, 2011)
  15. R Sayre and J Dowdy, Darkness at noon: Sunscreens and vitamin D3, Photochemistry and Photobiology 83 459–463 (2007)
  16. Diehl and Chiu, Effects of ambient sunlight and photoprotection on vitamin D status, Dermatologic Therapy 23 48–60 (2010)
  17. Terushkin et al, Estimated equivalency of vitamin D production from natural sun exposure versus oral vitamin D supplementation across seasons at two US latitudes, J Amer Acad Derm 929–934 (Jun 2010)
  18. Ibid Ref 1, pp 161
  19. H Brannon, Fitzpatrick classification scale, Dermatology, available at (Accessed Dec 29, 2011)
  20. Ibid Ref 1, pp 173
  21. US Pat 6,504,161, Radiation indicator device, assigned to Medinnovas Inc., available at (Accessed Dec 29, 2011)
  22. EG Todorov,, available at (Accessed Dec 29, 2011)
  23. J Mercola,, The surprising cause of melanoma (And no, it’s not too much sun), available at
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