We've covered the growing body of evidence that vitamin D is critical to health and disease prevention … see the Vitamin D section of our news archive … which includes 10 subsections covering everything from Immunity, Bone, Heart, and Brain Health to Sources, Intakes, Metabolic Health, Pregnancy, and Children.
Professor Holick on sun exposure and skin cancer
What about the risk of skin cancer from sun exposure?
Dr. Holick summarizes the evidence succinctly on his website:
“The sun has been demonized …. [but] …there is essentially no substantiated scientific evidence to suggest that moderate sun exposure either significantly increase risks of squamous and basal cell carcinomas, and more importantly, the most deadly form of skin cancer, melanoma.
“There is no question that excessive exposure to sunlight and sun-burning experiences significantly increase risk of both basal and squamous cell carcinoma. However, these cancers are often easily detected, and if detected early, are easily treated and often cured.
“Melanoma on the other hand, is a very aggressive and deadly form of skin cancer. However, most melanomas occur on the least sun-exposed areas, and a recent meta-analysis of 35 studies suggests that occupational exposure to sunlight decreases risk of developing melanoma.”
Earlier this decade, Dr. Holick and fellow vitamin D researchers published findings that deem vitamin D deficiency a public health disaster (Grant WB, Garland CF, Holick MF 2005):
“We estimate that 50,000-63,000 individuals in the United States and 19,000-25,000 in the UK die prematurely from cancer annually due to insufficient vitamin D.”
“The U.S. economic burden due to vitamin D insufficiency from inadequate exposure to solar UVB [ultraviolet B] irradiance, diet, and supplements was estimated at $40-56 billion in 2004, whereas the economic burden for excess UV irradiance was estimated at $6-7 billion.”
“These results suggest that increased vitamin D through UVB irradiance, fortification of food, and supplementation could reduce the health care burden in the United States, UK, and elsewhere.”
Now, a clinical study from cloudy Denmark further discredits the anti-sun war waged by official dermatology.
Danish scientists find sunscreen advice blocks vitamin D
According the authors of a study published in the British Journal of Dermatology, people who use the amount and sun protection factor (SPF) of sunscreen recommended by the World Health Organization (WHO) produce little or no vitamin D.
Their findings suggest that excessive, obsessive sunscreen use may lead to vitamin D deficiency.
Researchers from Copenhagen's Bispebjerg Hospital recruited 37 healthy volunteers with fair skin (Faurschou A et al. 2012).
The volunteers applied sunscreen that met WHO recommendations for thickness and SPF rating, and the Danish team measured the subjects' blood levels of vitamin D before and after exposure to ultraviolet B (UVB) radiation.
Fish fit the vitamin D bill; Sockeye salmon stand out
In addition to getting vitamin D from supplements, certain fish rank among the very few substantial food sources of vitamin D, far outranking milk and other D-fortified foods.
Among fish, wild sockeye Salmon rank as the richest source, with a single 3.5 ounce serving surpassing the US RDA of 600 IU by about 15 percent:
Vitamin D per 3.5 ounce serving*
Sockeye Salmon 687 IU
Albacore Tuna 544 IU
Silver Salmon 430 IU
King Salmon 236 IU
Sardines 222 IU
Sablefish 169 IU
Halibut 162 IU
*For our full test results, click here.
Sunscreen with an SPF of eight was applied at thicknesses – measured as milligrams per square centimeter of skin (mg/cm²) – that ranged from 0.5, 1, 1.5, or 2 mg/cm². Some of the volunteers applied no sunscreen, to serve as controls.
Every two to three days, the recruits' sunscreen-covered skin areas were exposed to UVB radiation equal to three “standard erythema (skin reddening) doses” 20 minutes after sunscreen application. This cycle was repeated four times.
The researchers found that the participants who'd applied thinner sunscreen layers produce more vitamin D after their UVB exposure.
However, vitamin D levels did not rise significantly in those treated with the thickest layer of sunscreen (2 mg/cm²) … which is the level recommended by the WHO.
As the authors wrote, “… we demonstrated that the vitamin D serum [blood] level increases in an exponential manner with decreasing thickness of sunscreen layer in response to UVB exposure.”
And they drew a reasonable conclusion: “Our results suggest that sunscreen use according to the current recommendations by the WHO may be re-evaluated” (Faurschou A et al. 2012).
Sensible vitamin D solutions:
Seafood, supplements, and moderate sun exposure
Dr. Holick's position is far from radical, and he's careful to say that people should avoid tanning and staying in the sun unprotected too long.
Fortunately, he's still Professor of Medicine in BU's Department of Physiology and Biophysics, where his stated goal – pursued in part via his book, “The Vitamin D Solution” – is to highlight the “vitamin D deficiency pandemic” and its harrowing implications for public health.
As Holick notes, “90-95% of most people's vitamin D requirement comes from casual exposure to sunlight. There needs to be a reevaluation of the important role that sensible sun exposure has in providing vitamin D for the world's population.”
Of course, you can get ample vitamin D from supplements and fatty seafood, with wild salmon, tuna, sardines, and mackerel being the richest food sources by far (see our sidebar, “Fish fit the vitamin D bill”).
Sockeye salmon is the best food source of all, with a whopping 687 IU per 3.5 oz serving. In 2010, the US RDA for people from age one to 70 was raised from 200 to 600 IU … see “Vitamin D RDAs Raised Substantially.”
But we also know that sun exposure is good for mood, and many people feel sad or even depressed when they get too little.
Do sunscreens prevent skin cancer?
Epidemiological studies have linked excessive sun exposure to risk of common, relatively non-threatening skin cancers … and sunscreens do seem to prevent these.
But there's little or no evidence that – absent certain melanoma risk factors (see below) – moderate exposure increases the risk of any kind skin cancer … see our sidebar, “Professor Holick on sun exposure and skin cancer.”
There's little evidence that sunscreens prevent the rarest and far more deadly form, called melanoma. But it's only been a decade since sunscreens began to protect against both kinds of UV radiation, including the UVA type thought to promote melanoma.
The melanoma-prevention message has been sun avoidance, especially at midday intensity, but things are not so clear-cut.
For example, there are more cases of melanoma in people living at northern latitudes, where the sun is less intense, than among people in southern latitudes.
Several factors other than sun exposure appear related to development of melanoma:
Numerous moles on the legs
Natural hair color is red or blond
Using artificial tanning lights once or more a month
Increasing number of sunburns from age 10 to 19
Heredity (two or more family members had melanoma)
Extremely rare skin disorder known as xeroderma pigmentosum
Weakened immune system due to another cancer, AIDS, or immune-suppressing drugs
Many researchers, including Dr. Holick, believe that another risk factor might be reliance on UVB-only sunscreens.
Until the late 1990s, all sunscreens protected only against UVB sunrays … the form of radiation that reddens the skin and is believed to cause the far more common non-melanoma skin cancers … basal-cell and squamous-cell carcinomas.
The use of UVB-only sunscreens led many people to stay in the sun but did not protect them against UVA sunrays, which cause wrinkles, and may cause melanoma.
Now, all sunscreens contain screens against UVA and UVB. However, the extent of UVA protection they provide remains uncertain and controversial, so it makes sense to exercise caution.
Basal cell carcinoma accounts for more than 90 percent of all skin cancers, is typically slow-growing, and seldom spreads to other parts of the body, while squamous cell carcinoma spreads slightly more often.
All skin cancers should be found and treated early because they can invade and destroy nearby tissue.
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Diffey BL. Sunscreens and melanoma: the future looks bright. Br J Dermatol. 2005 Aug;153(2):378-81.
Doré JF, Chignol MC. Tanning salons and skin cancer. Photochem Photobiol Sci. 2012 Jan;11(1):30-7. Epub 2011 Aug 15. Review.
Faurschou A, Beyer DM, Schmedes A, Bogh MK, Philipsen PA, Wulf HC. The relation between sunscreen layer thickness and vitamin D production after UVB exposure - a randomised clinical trial. Br J Dermatol. 2012 Apr 18. doi: 10.1111/j.1365-2133.2012.11004.x. [Epub ahead of print]
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Oliveria SA, Saraiya M, Geller AC, Heneghan MK, Jorgensen C. Sun exposure and risk of melanoma. Arch Dis Child. 2006 Feb;91(2):131-8. Epub 2005 Dec 2. Review.
Vainio H, Bianchini F. Cancer-preventive effects of sunscreens are uncertain. Scand J Work Environ Health. 2000 Dec;26(6):529-31.
Whiteman DC, Whiteman CA, Green AC. Childhood sun exposure as a risk factor for melanoma: a systematic review of epidemiologic studies. Cancer Causes Control. 2001 Jan;12(1):69-82. Review.