Cancer is used generically for more than 100 different diseases, including malignant tumors of different sites such as breast, stomach, colon, lung and mouth.【1】The disease arises principally as a consequence of individual exposure to the substances that cause cancer in what individuals inhale, eat and drink, or are exposed to in their personal or work environment. Personal habits, such as tobacco use, dietary and physical activity patterns—well as occupational and environmental conditions—rather than genetic factors, play the major roles in the development of cancer.
Many of the chronic diseases risk and the diseases themselves overlap. In developed countries, cancer is the second-biggest cause of death after cardiovascular disease (CVD), and epidemiological evidence points to this trend emerging in the less developed world. This is particularly true in countries of "transition" or middle income countries such as in South America and Asia. Already more than half of all cancer cases occur in developing countries.
There are approximately 20 million people living with cancer at the moment; by 2020 there will an estimated 30 million. And the impact is far greater than the number of cases alone would suggest.【2】Regardless of prognosis, the initial diagnosis is of- ten perceived by patients as life-threatening, with over one-third of sufferers experiencing clinical anxiety and depression. Cancer can also be profoundly distressing as well as economically disruptive to patients' families. The clinical care of cancer patients is a costly element in public health budgets.
【3】Dietary factors are estimated to account for approximately 30% of cancers in Western countries, making diet second only to tobacco as a preventable cause of cancer. This proportion is thought to be about 20% in developing countries and is projected to grow. As developing countries become urbanized, patterns of cancer, particularly those most strongly associated with diet and physical activity, tend to shift towards the patterns of economically developed countries. Cancer rates also change as populations move between countries and adopt different dietary patterns.
The relative importance of cancers as a cause of death is increasing. The incidence of lung cancer and cancers of the colon and breast generally increases in parallel with economic development, as stomach cancer declines. Cancer is also strongly associated with social and economic status. Cancer risk factors are highest in groups with the least education. In addition, patients in the lower socioeconomic classes have consistently poorer survival rates than those in higher social class.
In recent years, substantial evidence has pointed to the link from overweight and obesity, to many types of cancer such as breast and kidney.【4】The composition of the diet is also important since fruit and vegetables may have a protective effect by decreasing the risk for some cancer types such as oral and gastric cancer.
Regular physical activity has also been seen to have a protective effect in reducing the risk of breast cancer. High intake of preserved meat or red meat might be associated with increased risk of colorectal cancer. Another aspect of diet clearly related to cancer risk is the high consumption of alcoholic beverages, which convincingly increase the risk of oral cavity, liver and breast cancers.
The wealth of knowledge that already exists about cancer risk factors provides obvious and ample scope for action to reduce the cancer burden of all countries. After tobacco, overweight and obesity seems to be the most important avoidable cause of cancer.
【5】Given that poor nutrition, physical inactivity, obesity tobacco and alcohol are risk factors common to other chronic diseases such as CVD, type 2 diabetes, and respiratory diseases, conducting a cancer prevention program withi