A large prospective study has revealed that a higher intake of vitamin D in women is linked to a lower risk of early-onset colorectal cancer.
Colorectal cancer is the third most common cancer worldwide, accounting for an estimated 1.8 million new cases and over 880,000 deaths in 2018. However, the incidence of early-onset colorectal cancer (EOCRC), defined as colorectal cancer in those under 50 years of age, is increasing by approximately 7.9% per year among those aged 20 – 29 years. Moreover, EOCRC is more often diagnosed at an advanced stage. While the reasons for this are uncertain, it could be linked to sedentary behaviour or obesity. A further compounding factor, is the delay in seeking advice with one study in 1089 patients with EOCRC, reporting that nearly two-thirds of patients waited 3 – 12 months before seeking medical advice, with many indicating that they were initially misdiagnosed.
One potential protective factor against colorectal cancer is vitamin D and there is evidence of a strong inverse relationship between vitamin D levels and the risk of colorectal cancer. Nevertheless, whether reduced plasma levels of vitamin D are also associated with the development of early-onset colorectal cancer is uncertain. In trying to ascertain the relationship between these two factors, a team from the Department of Epidemiology, Harvard TH Chan School of Public Health, Boston, US, turned to the Nurses’ Health Study II which is a prospective cohort study of 116,429 female nurses aged between 25 and 42 years and which began in 1989. Study participants are followed every 2 years by self-administered questionnaires which captures information on demographics, lifestyle factors, the presence of co-morbidities etc and a food frequency questionnaire, every 4 years. For the present study, the researchers set the primary end point as the development of EOCRC, identified from medical records. In addition, the researchers collected data on the presence of adenomas and serrated polyps, which are pre-cancerous lesions. The plasma vitamin D levels were estimated based on factors such as dietary intake, age, race etc using a previously defined model.
A total of 94,205 women were included in the analysis and there were 111 documented cases of early-onset colorectal cancer detected between 1991 and 2015. The median vitamin D intake was 372 IU/day and vitamin D levels > 450 IU/day were associated with a reduced risk of developing EOCRC compared to intakes < 300 IU/day (hazard ratio, HR = 0.49, 95% CI 0.26–0.93). The HR per 400 IU/day increases was 0.46 (95% CI 0.26–0.83). Interestingly, the researchers also found that the HR for dietary vitamin D intake had a stronger inverse association with the development of EOCRC per 400 IU/day increase than among supplement users (0.34 vs 0.77, dietary vs supplements). There were 1439 newly diagnosed adenomas and 1878 serrated polyps in those aged less than 50 years and again, higher vitamin D intake was associated with a lower risk of developing either lesion.
The authors concluded that given the association between higher vitamin D intake and early-onset colorectal cancer, strategies to ensure adequate intake of the vitamin could serve as an important preventative measure in younger adults.
Kim H et al. Total Vitamin D Intake and Risks of Early-Onset Colorectal Cancer and Precursors. Gastroenterology. 2021