Protective effect from solar exposure, risk of an ecological fallacy

Basal cell skin cancer and the risk of second primary cancers: a cancer registry-based study in Lithuania

PURPOSE

The aim of this population-based cohort study was to determine the risk of second primary cancer in basal cell carcinoma (BCC) patients in Lithuania.

METHODS

This analysis was based on patients diagnosed with BCC in Lithuania between 1998 and 2007 and followed until 2011. Standardized incidence ratios for subsequent cancers as a ratio of observed number of cancer cases in people with previous BCC diagnosis to the expected number of cancer cases in the underlying general population were calculated.

RESULTS

After diagnosis of BCC, 1442 new cases of selected cancers were diagnosed. Compared with the general population, the incidence of all new primaries combined after BCC was very close to expected. Statistically meaningful increase in developing subsequent cancer was obtained for Hodgkin's lymphoma, prostate cancer, and leukemia in men, and for cancers of the lip, lung, and breast in women. Risk of melanoma and thyroid cancer was significantly elevated in both sexes. Relative risk of cancer of the eye was increased although not significant.

CONCLUSIONS

In our study, we found increased cancer risk for cancers related to sun exposure. In addition, increased risks were identified for Hodgkin's lymphoma, thyroid cancer, leukemia, prostate, and breast cancer in BCC patients.

Previous extensive sun exposure and subsequent vitamin D production in patients with basal cell carcinoma of the skin, has no protective effect on internal cancers

BACKGROUND

It has been suggested that sunlight through production of vitamin D might have a protective effect on a number of internal cancers. Consequently, in spite of the well known skin cancer risks, some researchers advocate more exposure to ultraviolet radiation, supported by the solarium industry. We estimated the risk of internal cancer before the patient contracted a basal cell carcinoma (BCC) of the skin, the most common cancer in white populations and strongly associated with extensive sun exposure.

METHODS

A nested case control study was undertaken in the whole Swedish population. 115,016 patients with BCC and 987,893 controls were linked to population based registers.

FINDINGS

The cases had an increased risk of getting another form of cancer before the BCC diagnosis: odds ratio (OR)=1.84; 95% confidence interval (CI) 1.81-1.86. This risk was mainly due to skin cancer: OR=4.95; 95% CI 4.81-5.09 but also non-skin cancer risk was elevated: OR=1.37; 95% CI 1.35-1.39. We adjusted the estimates for age, level of income, occupational status in national censuses, place of living and sex, where appropriate. Of the cancers specifically suggested to be related to vitamin D status: colon, prostate, breast, and ovary cancer, all had slightly increased ORs whilst for pancreatic and gastric cancer no increased OR was found.

INTERPRETATION

Patients with BCC, a proxy for extensive sun exposure, run an increased risk of other forms of cancer prior to the diagnosis of BCC. The findings in this study contradict that vitamin D production through extensive sun exposure has any protective effect on internal cancer but emphasise the increased risk for skin cancer.

The role of sunlight exposure in determining the vitamin D status of the U.K. white adult population

BACKGROUND

Vitamin D is necessary for bone health and is potentially protective against a range of malignancies. Opinions are divided on whether the proposed optimal circulating 25-hydroxyvitamin D [25(OH)D] level (≥ 32 ng mL⁻¹) is an appropriate and feasible target at population level.

OBJECTIVES

We examined whether personal sunlight exposure levels can provide vitamin D sufficient (≥ 20 ng mL⁻¹) and optimal status in the U.K. public.

METHODS

This prospective cohort study measured circulating 25(OH)D monthly for 12 months in 125 white adults aged 20-60 years in Greater Manchester. Dietary vitamin D and personal ultraviolet radiation (UVR) exposure were assessed over 1-2 weeks in each season. The primary analysis determined the post-summer peak 25(OH)D required to maintain sufficiency in wintertime.

RESULTS

Dietary vitamin D remained low in all seasons (median 3·27 μg daily, range 2·76-4·15) while personal UVR exposure levels were high in spring and summer, low in autumn and negligible in winter. Mean 25(OH)D levels were highest in September [28·4 ng mL⁻¹; 28% optimal, zero deficient (<5 ng mL⁻¹)], and lowest in February (18·3 ng mL⁻¹; 7% optimal, 5% deficient). A February 25(OH)D level of 20 ng mL⁻¹ was achieved following a mean (95% confidence interval) late summer level of 30·4 (25·6-35·2) and 34·9 (27·9-41·9) ng mL⁻¹ in women and men, respectively, with 62% of variance explained by gender and September levels.

CONCLUSIONS

Late summer 25(OH)D levels approximating the optimal range are required to retain sufficiency throughout the U.K. winter. Currently the majority of the population fails to reach this post-summer level and becomes vitamin D insufficient during the winter.

Nonmelanoma skin cancer and the risk of second primary cancers: a systematic review

BACKGROUND

Based on empirical evidence, a personal history of nonmelanoma skin cancer (NMSC) has been hypothesized to be a risk factor for other cancers. Others hypothesize that NMSC may be a marker of high cutaneous vitamin D synthesis and therefore inversely associated with risk of other malignancies. To reconcile these divergent views, we carried out a systematic review to determine the association between NMSC and subsequent risk of other cancers.

METHODS

Bibliographic databases were searched through March 2009. Studies were included if sufficient information was presented to estimate the risk of developing other cancers following NMSC. Studies were reviewed and data were abstracted independently in duplicate with disagreements resolved by consensus.

RESULTS

Of the 21 included studies, 15 reported the association between NMSC and risk of all other cancers combined. NMSC was significantly associated with increased risk of another malignancy among cohort studies based on cancer registries summary random-effects relative risk (SRR), 1.12; 95% confidence interval (CI), 1.07-1.17; n = 12 studies) and those with individual-level data (SRR, 1.49; 95% CI, 1.12-1.98; n = 3). In stratified analyses of registry studies, this association held true for both squamous (SRR, 1.17; 95% CI, 1.12-1.23; n = 7) and basal cell carcinoma (SRR, 1.09; 95% CI, 1.01-1.17; n = 7), and both men (SRR, 1.14; 95% CI, 1.09-1.20; n = 12) and women (SRR, 1.10; 95% CI, 1.04-1.15; n = 12).

CONCLUSIONS

Strong, consistent evidence indicates that a personal history of NMSC is associated with increased risk of developing other malignancies.

IMPACT

For unknown reasons, NMSC may be a risk factor for other cancers.

Review article: vitamin D acquisition and breast cancer risk

OBJECTIVE

The aim of the study was to focus on the association of vitamin D and breast cancer.

METHODS

The study of evidence concerning vitamin D's influence on the origin and development of breast cancer from a PubMed and individual searches.

RESULTS

Body sunlight exposure may reduce the prevalence of breast cancer. However, these studies correspond to global populations of different countries and regions without considering other geographic factors and individual, ethnic, and cultural factors that may affect sunlight exposure. Epidemiological analyses show that low vitamin D ingestion is associated with increased risk of breast cancer. Studies measuring serum vitamin D metabolites in women who were followed many years suggest that low circulating 25-hydroxyvitamin D3 levels are associated with increased breast cancer risk.

CONCLUSIONS

Although there are controversial results, it seems plausible that sufficient endogenous vitamin D levels may have a protective function on mammary cells, reducing breast cancer risk.