Life-long Vegetarianism and Colorectal Cancer
Background
Colorectal cancer rates are much lower in India than in Western countries. The high incidence in the West is attributed mainly to dietary factors (high red meat intake and low fibre being particularly implicated). Results have not been consistent, however, possibly due to the relative homogeneity of Western diets. Indian populations, in contrast, are characterised by larger variability in dietary intakes and a significant proportion (about 25%) are lifelong vegetarians for religious reasons. Studies in Western populations investigating the association between vegetarianism and colorectal cancer have produced conflicting results.
Aim
To investigate the association between life-long vegetarianism and risk of colorectal cancer in India.
Methods
A hospital-based case-control study was carried out at the Tata Memorial Centre in Mumbai, India. Cases were defined as newly diagnosed, histologically confirmed colorectal cancer with controls selected from the relatives and visitors of non-colorectal cancer patients. Controls were frequency matched to the cases by age, sex and region of permanent residence. A structured questionnaire was administered by a trained interviewer. Odds ratios were calculated using logistic regression in STATA.
Results
- 409 cases and 737 controls were recruited between 2007 and 2009.
- The percentage of life-long vegetarians was 24.2% amongst cases and 37.3% amongst controls.
- Life-long vegetarianism was found be associated with a reduced risk of colorectal cancer with an overall OR of 0.53 (95%CI 0.38-0.73) after adjusting for age, sex, region, religion, education, socioeconomic factors, diabetes, smoking, alcohol and intake of pulses, fruits, vegetables & dairy products.
- There was significant variation in the odds ratio found for different states, as shown in Table 1 and Figure 1.
Figure 1. Odds ratio, 95% Confidence Intervals, p values and number of cases and controls in individual states.
Table 1. Odds ratio, 95% Confidence Intervals , p values in individual states.
| State | Odds ratio (95% Confidence Intervals ) | p value |
|---|---|---|
| Maharashtra | 0.80 (0.50 – 1.27) | 0.34 |
| Madhya Pradesh | 0.74 (0.20 – 2.72) | 0.65 |
| Uttar Pradesh | 0.69 (0.28 – 1.69) | 0.69 |
| Orissa | 0.08 (0.01 – 1.13) | 0.08 |
| Bihar | 0.18 (0.05 – 0.72) | 0.18 |
| West Bengal | 0.22 (0.05 – 0.90) | 0.22 |
| Assam | 0.76 (0.07 – 7.87) | 0.82 |
Conclusion
- In this case-control study, life-long vegetarianism appears to reduce the risk of developing colorectal cancer in an Indian population.
- Although the ORs in individual states were all less than 1.0, the significant variation found is likely to be due to referral bias.
- Recall bias is unlikely to have been a factor in the measurement of the primary exposure variable of life-long vegetarianism.
