(1) When studying the relationship between diet, lifestyle or environmental factors and diseases, we seldom get definite results, and some even get contradictory results.
For example, Dai Wencan thinks that passive smoking is an important risk factor for female lung cancer, while Xu Zhaoyi and others give a negative answer. There are also many reports on the relationship between indoor radon and lung cancer, pesticide residue and breast cancer, high voltage electromagnetic field and brain cancer, lymphoma and leukemia.
(2) It is difficult to distinguish low risk factors from confounding factors. RR(OR)& lt； 2% of low-risk factors often exist in chronic diseases, which can be concealed by high-risk factors, and may also be interfered by biased and mixed factors. This kind of deviation and confusion can come from many aspects, such as inquiry deviation, answer deviation, choice deviation, will deviation, wrong classification deviation, memory deviation, publication deviation and so on. It may also be caused by the interaction between different factors and various factors. However, the role of low-risk factors can not be ignored, especially in high-risk diseases. For example, if the incidence of a disease is 12% and its RR is 1.2, 2,000 patients can be added among 654.38+10,000 people.
(3) Some risk factors are not supported by biological rationality, so it is difficult to properly explain the causes and distribution of diseases. For example, smoking in lung cancer mainly induces squamous cell carcinoma, while reports that passive smoking can induce lung cancer are mostly adenocarcinoma. For another example, air pollution caused by coal burning has existed in China for hundreds of years, while female lung cancer has increased rapidly in the past 30 years. The indoor air pollution in eastern and western countries is very different, but the situation of female lung cancer is very similar.
(4) Pay attention to positive results and despise negative results and low risk factors; Pay attention to the risk factors that lead to diseases and ignore the protective factors that inhibit the occurrence of diseases; Attaching importance to environmental risk factors while ignoring their own genetic factors hinders the in-depth study and reasonable explanation of the causes of diseases. In recent years, in-depth study on the etiology of lung cancer found that eating more fresh vegetables and fruits has a protective effect on lung cancer. High-fat diet, especially foods rich in saturated fatty acids, is a risk factor for lung cancer, and its or value can be as high as 1 1 in non-smoking women. After studying the etiology of lung cancer in seven cities in Liaoning Province, Xu Zhaoyi and others think that smoking can only explain the incidence of lung cancer in two-thirds of men and13 of women, and the growth of lung cancer in men and women should be found from the factors that have acted on both men and women in the last two or three decades, such as diet structure, genetic factors, susceptibility and resistance of the body, endocrine function and so on. WUAH et al. conducted a population-based multi-factor study in the United States, and found that the risk of respiratory cancer in the first-degree relatives of lung cancer patients increased by 30% (95% Cl 0.9 ~ 1.8), and the risk of female relatives of lung cancer patients increased by 3 times, and this increase was not affected by smoking history.