Differences in colon cancer incidence rates by latitude.
e14627 Background: There is significant decrease in the ultraviolet B photons reaching the earth’s surface during November to February (Holick MF Am J Clin Nutr. 2004 Dec; 80(6 Suppl):1678S-88S). This results in little if any vitamin D3 production in the skin during this period. This study was conducted to evaluate difference in colon cancer age adjusted incidence rates in the northern (latitude ≥37o N) and the southern (latitude < 37oN) regions in the contiguous United States during 1973-2008. Methods: Patients, aged 20 years and older, who had been diagnosed with colong cancer during January 1973 and December 2008, were selected from the Surveillance, Epidemiology, and End Results (SEER) 13 database. Based on the counties’ centroid, northern (latitude ≥37o N) and southern (latitude < 37oN) regions were determined. We compared age adjusted incidence rates (AAIR) of colon cancer in the southern and northern regions among cohorts of patients categorized by age (≥20, 20-64, ≥65 years), gender (Men, Women) and Race (Caucasians, Blacks, Others). The AAIR was calculated per 100,000 population. We used SEER*Stat software to calculate age adjusted incidence rate, incidence ratio, confidence interval (CI, 95%) and P value. Results: There were 314,975 cases of colon cancer diagnosed among 608,245,557 US population during 1973-2008. The overall colon cancer AAIR was 57.1 per 100,000 population studied. The incidence rates were 49.1 in the south and 58.7 in the north of 37oN latitude, (95% CI 1.18-1.20, p<0.05). The AAIRs for patients in the age group 20-64 years were 17.9 and 18.8 in the southern and northern regions, (CI 95%, 1.0346-1.0697), p<0.0005 respectively. The incidence rates for patients aged ≥65 years were 194.3 and 243.9 in the southern and northern regions, (CI 95%, 1.0346-1.0697) p<0.0005. Similarly, the AAIRs were significantly higher in the northern region compared to southern region for both sexes and all ethnic groups. Conclusions: Colon cancer age-adjusted incidence rate is significantly higher in the Northern compared to the Southern region of the US. The higher incidence of colon cancer in the North may be related to lack of sunlight exposure and relative vitamin D deficiency.