Vitamin D Insufficiency Due to Insufficient Exposure to Sunlight and Related Pathology

Limiting the use of sunscreen is another way to increase an individual’s vitamin D level. Within the past thirty years, sunscreen use has been encouraged in order to reduce the incidence of skin cancers. While solar radiation still poses this risk, overcompensation with sunscreen has been shown to severely limit an individual’s capacity to produce naturally-occurring vitamin D. According to Mittelstaedt, “while there is a risk of skin cancer from overexposure to ultraviolet light, […] the benefits of modest sun exposure in preventing serious, hard-to-treat cancers outweighs that risk. Furthermore, […] skin cancer is relatively easy to treat.” A suggested compromise for sunscreen users is to spend five or ten minutes in the midday sun without the sunscreen, then apply as normally directed. This brief amount of exposure is enough to synthesize of weeks’ worth of vitamin D.

It is possible to obtain vitamin D through naturally-occurring dietary sources. However, there are very few foods that contain vitamin D, some of which are: cod liver oil (1300 IU per tablespoon); wild salmon (1000 IU per serving); farmed salmon (250 IU); sardines (600 IU); fortified milk or orange juice (100 IU); egg yolk (25 IU); fresh shiitake mushrooms and some organ meats (traces in both) (Mittelstaedt, 2008). Considering that there is a debate regarding the appropriate amount of daily vitamin D, it may or may not be reasonable to obtain all of the necessary vitamin D from dietary sources. The US dietary recommendation for vitamin D is not clearly defined. According to the U.S. Department of Health and Human Services, individuals who are at higher risk of vitamin D insufficiency, such as individuals with dark skin or those who are housebound, should increase their daily intake to 1000 IU, but there is no specified guideline for the daily vitamin D intake for individuals of lower risk. The health.gov website also specifies that “optimal serum 25-hydroxyvitamin D may be as high as 80 nmol/L”, which provides clinicians with a benchmark to measure their patients’ relative risk. Canada has recently increased their RDA to 1000 IU daily year-round for non-white adults, and 1000 IU daily in the fall and winter for white adults.

Supplementation is a valid way for many individuals to reach their recommended daily intake of vitamin D.  According to Bordelon, et al (2009), “evidence shows that vitamin D supplementation of at least 700 to 800 IU per day reduces fracture and fall rates in adults.”

Toxicity of Vitamin D

It is important to note that it is possible to have too much vitamin D in the body. However, the point at which vitamin D becomes toxic is a point of contention. It is widely accepted that vitamin D produced in the skin as a result of sun exposure “is not known to result in toxic levels” (Blake, 2007).  This is because levels produced in the skin are self-adjusting based on the body’s needs.

Vitamin D toxicity is known as hypervitaminosis D. Extremely high blood levels of vitamin D can cause abnormally high blood calcium levels. This can cause some of the conditions that vitamin D is usually prescribed to prevent, including bone loss. According to Blake (2007), “ long-term overconsumption of vitamin D can cause calcification of organs such as the heart, blood vessels, and the kidneys.” However, vitamin D toxicity is unlikely in healthy adults who are consuming fewer than 10,000 IU of vitamin D through supplements each day. The widely accepted Upper Intake Level (UL) of vitamin D is approximately 2000 IU per day via supplementation, but this figure is being examined as vitamin D’s benefits are being studied more and more.

According to Cannell (2008),

“One could compare vitamin D toxicity to water intoxication. For example, 8 glasses of water a day is recommended consumption. However, regular consumption of 80 glasses a day can be fatal. So you could say that water has a therapeutic index of 10 (80/8). Most vitamin D experts now say that humans should get about 4,000 units of vitamin D a day (from all sources), but 40,000 units a day will hurt them (over several years). Therefore, vitamin D has a therapeutic index of 10 (40,000/4,000), the same as water. Although we are not saying it is as safe as water, we are saying vitamin D is safe when used in the doses nature uses it.” 

Conclusion

All of the recent research on vitamin D can be overwhelming, and it is important to remember that vitamin D’s effectiveness in preventing or reversing disease is still being studied.  Many of the so-called “latitude studies” are observational studies that “use ambient solar UV radiation as a proxy for latitude and Vitamin D status. For these studies, researchers compare rates of certain major cancers  […] to rates of sunlight exposure. This group of research has the liability of being wildly inconsistent.” (Marshall Protocol Knowledge Base, 2010). That is to say, studies that extrapolate data based on correlation may not draw the correct conclusion. A researcher cannot draw conclusions regarding causation simply by looking at a map.

It is clear that more research needs to be done in order to establish reliable guidelines on Vitamin D3 levels for all populations. Because Vitamin D3 supplements are very inexpensive, there is likely no pharmaceutical company that will spearhead the research required, and it seems that the Federal Government will eventually need to take up this cause. However, even without further research, it is known that low vitamin D levels can be detrimental, and persons with one or more risk factors would benefit from speaking to their physician about this issue.

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