Lifestyle Interventions in the Prevention and Treatment of Cancer

Clarence H. Brown III, MD; Said M. Baidas, MD; Julio J. Hajdenberg, MD; Omar R. Kayaleh, MD; Gregory K. Pennock, MD; Nikita C. Shah, MD; Jennifer E. Tseng, MD

Disclosures

Am J Lifestyle Med. 2009;3(5):337-348. 

In This Article

Skin Cancers

Worldwide, the incidence of melanoma is increasing at a rate faster than any other malignancy. One in 5 Americans will develop skin cancer during their life-time. An estimated 1 in 63 Americans will develop melanoma, and this risk is 1 in 33 if in situ melanomas are included.[101] Melanoma incidence is increasing across all age groups. It is now the second most common cancer in women in their 20s and third most common cancer in men in their 20s.[101] More than 1 million new skin cancers will be diagnosed this year in the United States, but actual numbers are likely higher and underreported. It is estimated that $500 million is spent annually in the treatment of skin cancers in the United States.[101]

Ultraviolet (UV) radiation has been demonstrated to be both mutagenic and carcinogenic in many in vitro and in vivo studies. Its damaging effects on molecules and cellular structures have been well demonstrated. Skin cancer develops because DNA is altered after exposure to UV radiation.[102] Ultraviolet B (UVB) radiation has a long-accepted role in the development of skin cancers. UVB radiation, by virtue of its short wave-length (<320 nm), is absorbed through-out the epidermis, including proteins and DNA.[103] The carcinogenic effects of UVB radiation occur through direct absorption of photons, but it is also known that UVB radiation damages proteins and cell membranes, in addition to generating oxidative stress.[104,105]

The role of ultraviolet A (UVA) radiation in the development of malignancy and immunosuppression has recently become more clear.[105,106] UVA radiation, with its longer wavelength (320-400 nm), more easily penetrates the skin, even reaching the basal layer of the epidermis, including dermal fibroblasts. The integrity of the genetic code is maintained by DNA repair mechanisms, which allow damaged bases or altered gene sequences to be eliminated and replaced via base and nucleotide excision repair pathways.[103] If DNA damage gets to a certain point and repair enzymes are saturated, signaling path-ways can be stimulated, and hyperproliferation of abnormal cells and subsequent tumor development may occur.[103,107,108]

The more common skin cancers, basal cell carcinoma and squamous cell carcinoma, most commonly occur on sun-exposed areas of skin. The risk is highest among those who burn easily.[109,110,111] Skin cancer risk is highest among those with fair skin. These individuals are more sensitive to exposure at wavelengths 290 to 320 nm.[112]

The incidence of skin cancer worldwide is highest in those areas with above-average annual UV radiation.[113] Mortality rates from melanoma in the United States and Canada have also been shown to directly correlate with ambient UV exposure, and this correlation is even higher when ambient UVA (320-400 nm) radiation is included.[114,115]

There is a direct correlation with basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) incidence and latitude, as demonstrated by Scotto et al.[116] There is a strong inverse correlation between latitude and incidence of BCC and SCC for both men and women. Long-term chronic UV exposure seems to increase the risk of nonmelanoma skin cancer, where the opposite (acute intermittent UV exposure) increases the risk of melanoma.[117] The incidence of melanoma is also higher in high-altitude regions, possibly related to higher UV fluencies (measured in J/cm2) in these areas.[118]

A complex study by Fears et al[119] demonstrated that when life-time residential history was coupled with levels of midrange UV radiation (UVB flux) to provide a measure of individual exposure to sunlight, a 10% increase in annual UVB flux was associated with a 19% increased risk of melanoma. Even in women who could tan easily, a 10% increase in hours out-doors was associated with a 5.8% increase in melanoma incidence. The influence of sun exposure in early life appears to be greater than exposure at a later age. Migration studies of people born in Australia demonstrate an increased risk of skin cancer compared to native Northern Europeans who migrated to Australia at age 10 years or older.[120] Nevertheless, UV exposure at later age also contributes to the risk of developing skin cancer. In patients before and after age 15 years, investigators demonstrated a similar upward gradient of melanoma related to the frequency of sunburns. Importantly, more than 5 sunburns doubled the melanoma risk, regardless of age at which the sunburns occurred.[121]

In areas of the skin consistently exposed to UV, such as the head and neck, the density of skin cancer is highest. In rarely exposed areas such as the scalp and buttocks, skin cancer development is rare.[122] In women, melanoma is more common on the lower extremities, where there tends to be more UV exposure, than in men.[123] Individuals with higher number of nevi (personal nevus count) have a higher risk of melanoma.[124]

Protection from UV exposure can lower subsequent skin cancer risk.[125] Sunscreens offering broader spectrum protect skin better from UV-induced neoplasia. In fact, daily use of broad-spectrum sun-screens significantly reduces UV-induced skin damage.[126] In children who regularly used sunscreens, lower nevus counts were found than in children who used less sun protection, thus suggesting that sun protection during childhood does reduce subsequent melanoma risk.[127] A meta-analysis of 11 studies of melanoma risk and sunscreen use showed only a small protective advantage.[128] However, when more recent studies are included where high sun protection factor sun-screens are available, a protective effect is identified, and other inherent flaws associated with retrospective studies may be responsible for protection not being American Journal of Lifestyle Medicine noted.[129] It is important that development of future sunscreens incorporates a full range of UV protection.[130]

In addition to sunscreen, patients are advised to wear protective clothing and avoiding sun exposure during peak (mid-day) hours when UV intensity is greatest. These interventions, coupled with regular sunscreen use, have the greatest impact in lowering skin cancer risk.[131] According to the National Institutes of Health, "exposure to sunlamps or sunbeds is known to be a human carcinogen."[132] In a case control study, the incidence of SCC and BCC was significantly associated with the use of any tanning device.[133] In a prospective cohort study of more than 100 000 Scandinavian women, a 55% increased melanoma risk was demonstrated in those who used tanning devices at least once a month between the ages of 10 and 39 compared to those who rarely or never used such devices.[134]

There are more than 50 000 tanning facilities in the United States, generating revenue of approximately $5 billion.[135] Of the 1 million people who use tanning salons every day, 70% are women between the ages of 16 and 49.[136] Tanning beds emit both UVA and UVB radiation.[137] In fact, the UVA irradiation emitted by some tanning beds may be 10 to 15 times higher than that of the midday sun. The idea that "controlled" salon tanning is safer than "uncontrolled" beach tanning is inaccurate.[137]

According to the International Agency for Research on Cancer, the use of tanning beds was positively associated with melanoma, particularly if first exposure occurred before the age of 35.[138] In a recent survey of non-Hispanic white teenagers (ages 13-19 years), 24% of respondents reported using a tanning facility at least once in their lives, and 28% of American teenage girls reported having used tanning salons 3 or more times during their lives.[136] Among children ages 11 to 18 years, 10% reported using indoor tanning sunlamps within the past year.[139] Twenty-eight states have regulations limiting teenagers' access to tanning facilities. In 2007, 16 more states introduced similar bills.[140] In some states, written parental consent is required for minors using commercial tanning beds. The Colorado House rejected a Senate-passed bill prohibiting anyone younger than age 18 years from using a tanning bed without a doctor's prescription, notarized parental consent, or parents present at the salon. In California, laws were recently passed prohibiting those ages 14 to 18 years from using any ultraviolet tanning device without written parental consent. In that state, tanning bed use under the age of 14 years is already banned.[141]

The Indoor Tanning Association, a vehement industry group, states that its mission is to "protect the freedom of individuals to acquire a suntan, via natural or artificial light. When it involves a suntan, the State has no business inserting itself between child and parent. This notion that government knows more about child rearing than parents is preposterous."[142,143] The International Agency for Research on Cancer,[137] American Academy of Pediatrics,[144] World Health Organization,[145] American Medical Association,[146] and American Academy of Dermatology[147] have all issued position statements against the use of tanning beds.

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