There is a strong evidence that human papillomavirus (HPV) is the key causative agent of cervical cancer. However, the majority of women who are exposed to the oncogenic HPV do not develop invasive cervical cancer, suggesting that other factors could play a role in the cause and progression of cervical cancer. Epidemiological studies have suggested carotenoids and retinol as possible risk co-factors in cervical cancer etiology. However, the evidence is not conclusive. The study was design to achieve five objectives: 1) to validate the food frequency questionnaire (FFQ) used in a case-control study in Bangkok, Thailand; 2) to examine the association of individual plasma carotenoids and retinol with the risk of in situ cervical carcinoma; 3) to examine association of individual plasma carotenoids and retinol with the risk of invasive cervical carcinoma; 4) to investigate the association between individual plasma carotenoids and retinol and the risk of progression from in situ carcinoma to invasive disease; 5) to investigate the association between concordant quartiles of the β-carotene as measured from plasma and dietary intake with risk of invasive cervical cancer. The FFQ measures reflect longer-term usual intake while plasma carotenoid measures reflect recent intake.
Included in the study were 50 in situ cases with abnormal Pap smears and pre-admission diagnosis of carcinomas in situ and 103 clinic controls with normal Pap smear test. Also included in the study were 201 invasive cases with histologically confirmed invasive cervical carcinoma and 302 hospital controls admitted to Siriraj Hospital with other unrelated diseases to cervical cancer. Plasma carotenoids and retinol were measured by high performance liquid chromatography (HPLC). Human papillomavirus infection was detected using a standard PCR-based test. Food frequency questionnaire (FFQ) was used to capture the intake of the β-carotene.
Results showed that:
1. After adjusting for age and body mass index (BMI), selected plasma carotenoids were moderately correlated with fruits and vegetable intake as well as nutrient intake.
2. In the age-adjusted and multivariate logistic regression models we found no significant associations between any of the plasma measures (carotenoid and retinol) and either risk of in situ or invasive disease as compared to controls or for in situ carcinomas versus invasive disease, a measure of disease progression.
3. Women high in both measures of exposure (dietary and plasma) for β-carotene were at significantly reduced risk of invasive cervical cancer after confounders were adjusted for in the multivariate logistic regression.
4. Women high on dietary intake and low on plasma for β-carotene were also at the lowest risk of invasive cervical cancer after adjusting for confounders.
Based on the results above, the study suggests that the FFQ used in Bangkok, Thailand is an acceptable tool for long-term dietary intake assessment. However, an additional validation study is warranted using large a sample size and participants that are more representative of the general population in Thailand. Furthermore, this study does not support the possibility of individual carotenoids and retinol as risk factors for in situ and invasive cervical carcinomas as well as the progression of cervical cancer to invasive disease. Lastly, the study suggests that long-term increased consumption of fruits and vegetables may provide some protection in women in Thailand from having invasive cervical cancer. However, additional research is needed to support this finding from our study
