4. Aims of the study

Dietary factors have been suggested to be significant determinants in the development of breast cancer. However, despite the extensive amount of study, only a few consistent findings between diet and breast cancer have emerged. In fact, there exists no realistic preventive strategy to reduce the high incidence of breast cancer. Identification of lifestyle factors that women themselves could influence would greatly help in developing such a strategy.

The main aims of this dissertation are:

1. To examine whether body-size indicators are associated with risk of premenopausal and postmenopausal breast cancer (I).

2. To assess how well the food frequency questionnaire designed for this study measures food consumption and nutrient intake (II).

3. To examine associations between the consumption of certain foods and risk of premenopausal and postmenopausal breast cancer (III).

4. To examine whether fat, fatty acids, fiber, or certain vitamins/antioxidants are associated with risk of premenopausal and postmenopausal breast cancer (III).

5. To assess the reporting bias resulting from the threat of disease, and how it influences the interpretation of the results on associations between dietary factors and risk of breast cancer (III).

6. To examine whether current and past alcohol consumption is associated with risk of premenopausal and postmenopausal breast cancer (IV).

7. To examine whether toenail selenium concentration is associated with risk of premenopausal and postmenopausal breast cancer a decade after the beginning of selenium supplementation of fertilizers in Finland (V).