Higher Fat Intake Associated With Lower Risk for Skin Cancer

Higher Fat Intake Associated With Lower Risk for Skin Cancer CME

News Author: Laurie Barclay, MD
CME Author: Désirée Lie, MD, MSEd


May 30, 2006 ?- Fat in the diet does not increase the risk of skin cancer and may even reduce the risk, according to the results of a case-control study published online in the May 29 issue of BMC Cancer. The investigators speculate that earlier studies showing benefits of low-fat diets were confounded by increased consumption of protective fruits and vegetables.

"Human studies of dietary fat as a possible risk factor for cutaneous malignant melanoma (CMM) and non-melanoma skin cancer (NMSC) ?- principally basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) ?- have produced inconsistent results," write Robert H. Granger, DrPH, MPH, BMedSci, from Menzies Research Institute in Hobart, Tasmania, Australia, and colleagues. "Experimental studies on mice provide evidence that dietary fat in general, and polyunsaturated fat in particular, may enhance the carcinogenic effects of ultraviolet radiation. A dietary intervention study demonstrated that reduction in fat intake reduces risk of NMSC, but the evidence from observational studies has been mixed."

This population-based study involved 652 histopathologically confirmed cases of CMM, BCC, and SCC from the Tasmanian Cancer Registry (TCR) and a common set of 471 controls selected at random from the state's electoral roll. The investigators compared subjects categorized by thirds of dietary fat intake score measured by the "Dobson short fat questionnaire," using logistic regression models adjusting for age, sex, skin type, and usual sun exposure. All subjects were then followed for 56 to 80 months until August 31, 2004, for a new NMSC, using record linkage with both the TCR and the Births, Deaths, and Marriages Registry.

Compared with subjects in the lowest fat intake category, those in the medium fat intake category had an odds ratio (OR) comparing cases and controls of 0.76 (95% confidence interval [CI], 0.56 - 1.03. For high fat intake, the OR was 0.62 (95% CI, 0.45 - 0.85), and the trend was significant (P < .01) for reduced OR with higher category dietary fat intake. For cases, the incidence rate ratio (IRR) relative to those in the lowest fat intake group was 0.72 (95% CI, 0.50 - 1.03) for medium fat intake, and 0.82 (95% CI, 0.56 - 1.20) for highest fat intake (linear trend, P = .30).

"Using the same dietary instrument with two study designs in the same Caucasian population, we found no evidence that high fat intake increases the risk of developing melanoma or non-melanoma skin cancers," the authors write. "Instead, our results suggest a risk reduction for high fat intake."

Study limitations were inability to adjust for total energy consumption, imprecision of the dietary fat assessment instrument, and possibility of residual confounding.

The authors write that conflicting results suggesting benefits of low-fat consumption in earlier studies may reflect "an increase in consumption of fruit and vegetables that are recognized as playing a protective role in many types of cancers, leaving open the possibility that the risk reduction found in that study is attributable, in part, to dietary factors other than reduced fat intake."

Menzies Research Institute supported its staff to conduct this analysis and write the paper from internal funds. The authors report no relevant financial relationships.

BMC Cancer. Published online May 29, 2006.
Learning Objectives for This Educational Activity
Upon completion of this activity, participants will be able to:

* Describe the association between skin cancer and dietary fat intake.
* Identify body type risk factors associated with skin cancer risk.

Clinical Context

According to the authors of the current study, dietary fat may act as a promoter of carcinogenesis and may enhance the carcinogenic effects of ultraviolet radiation, but evidence from observational studies on skin cancer has been mixed and inconsistent. According to the authors, no study has to date examined the relationship between dietary fat intake and risk of CMM, BCC, and SCC.

This combined case control and cohort study involving patients diagnosed with one of these skin cancers and a control group without skin cancer, in Tasmania, examines the relationship between dietary fat intake and incidence of skin cancer. The cohort study followed patients from baseline for 56 to 80 months for incidence of skin cancer.
Study Highlights

* Subjects were aged 20 to 59 years of northern European ancestry (ie, white) who lived in the state of Tasmania at a latitude of 41° to 44°south.
* Eligible cases of CMM were ascertained from the Tasmanian Cancer Registry (TCR); cases of BCC and SCC were a random sample reported to the registry. Controls were randomly selected from the state electoral roll.
* Of those invited to participate, 90.1% of patients with CMM, 88.2% of BCC, and 88.1% of SCC, and 80.7% of control patients responded, for a total of 652 cases and 471 controls.
* Subjects were followed for 56 to 80 months and subsequent skin cancers and deaths were identified from the TCR and the Birth, Deaths, and Marriages Registry.
* In the case control study, subjects completed a baseline questionnaire and physical examination.
* Questions addressed hours of sun exposure throughout life, frequency of outdoor activities, and self-assessed hair color and skin sensitivity. Physical examination included anthropometric measurements, spectrophotometric cutaneous melanin density, skin and eye color, and count of nevi and freckles.
* Dietary fat intake was assessed using the Dobson short fat questionnaire, which ranks fat intake in 3 categories (1-21, 22-28, and 29-51 points). Fat intake scores were given based on responses to 17 questions.
* Amounts of intake of total unsaturated, polyunsaturated, and other types of fat were not quantified.
* 96% of those with baseline skin cancer and 96% of control subjects had complete data and were followed up and analyzed.
* Analysis was adjusted for sex, age, skin melanin, and socioeconomic status.
* Mean age at baseline was 45 years, half of the participants were men, mean body mass index was 27 kg/m2, and mean weight was 83 kg for men and 70 kg for women. The mean number of self-reported sports activities each summer in 7 sun-based activities was 4.6 for men and 1.7 for women.
* Controls had higher sex-adjusted mean values for fat intake (score of 25.9) compared with CMM, BCC and SCC cases (24.5, 24.9, and 24.3, respectively).
* BCC and SCC cases had higher socioeconomic status. CMM cases had higher waist-to-hip ratio.
* Cases of CMM, BCC, and SCC were less likely to have higher fat intake than controls.
* For all cases of skin cancer, the OR for the cases compared with controls was 0.76 for fat intake score of 22-28 points and 0.62 for fat intake score of 29-51 points.
* High waist-to-hip ratio was associated with reduced risk of BCC (P < .01) with an OR of 0.83.
* Other body size indices and socioeconomic status were not associated with skin cancer risk.
* Higher dietary fat category was associated with lower subsequent sex, age, and melanin-adjusted incidence of non-melanoma skin cancer than a low dietary fat intake.
* For all types of skin cancer, the incidence rates compared with those with the lowest fat intake score (1-21 points) were 0.72 for those with fat intake scores of 22-28 points and 0.82 for those with fat intake scores of 29-51 points.

Pearls for Practice

* Higher fat intake is associated with lower risk for skin cancer.
* High waist-to-hip ratio, but not body mass index or other measures of body size, is associated with reduced risk of BCC.

Medscape online