Elsevier

Biomedicine & Pharmacotherapy

Volume 61, Issue 10, December 2007, Pages 640-658
Biomedicine & Pharmacotherapy

Dossier : Cancer : Influence of environment
Lifestyle-related factors and environmental agents causing cancer: An overview

https://doi.org/10.1016/j.biopha.2007.10.006 Get rights and content

Abstract

The increasing incidence of a variety of cancers after the Second World War confronts scientists with the question of their origin. In Western countries, expansion and ageing of the population as well as progress in cancer detection using new diagnostic and screening tests cannot fully account for the observed growing incidence of cancer. Our hypothesis is that environmental factors play a more important role in cancer genesis than it is usually agreed. (1) Over the last 2–3 decades, alcohol consumption and tobacco smoking in men have significantly decreased in Western Europe and North America. (2) Obesity is increasing in many countries, but the growing incidence of cancer also concerns cancers not related to obesity nor to other known lifestyle-related factors. (3) There is evidence that the environment has changed over the time period preceding the recent rise in cancer incidence, and that this change, still continuing, included the accumulation of many new carcinogenic factors in the environment. (4) Genetic susceptibility to cancer due to genetic polymorphism cannot have changed over one generation and actually favours the role of exogenous factors through gene–environment interactions. (5) Age is not the unique factor to be considered since the rising incidence of cancers is seen across all age categories, including children, and adolescents. (6) The fetus is specifically vulnerable to exogenous factors. A fetal exposure during a critical time window may explain why current epidemiological studies may still be negative in adults. We therefore propose that the involuntary exposure to many carcinogens in the environment, including microorganisms (viruses, bacteria and parasites), radiations (radioactivity, UV and pulsed electromagnetic fields) and many xenochemicals, may account for the recent growing incidence of cancer and therefore that the risk attributable to environmental carcinogen may be far higher than it is usually agreed. Of major concern are: outdoor air pollution by carbon particles associated with polycyclic aromatic hydrocarbons; indoor air pollution by environmental tobacco smoke, formaldehyde and volatile organic compounds such as benzene and 1,3 butadiene, which may particularly affect children and food contamination by food additives and by carcinogenic contaminants such as nitrates, pesticides, dioxins and other organochlorines. In addition, carcinogenic metals and metalloids, pharmaceutical medicines and some ingredients and contaminants in cosmetics may be involved. Although the risk fraction attributable to environmental factors is still unknown, this long list of carcinogenic and especially mutagenic factors supports our working hypothesis according to which numerous cancers may in fact be caused by the recent modification of our environment.

Introduction

Lifestyle-related factors are not by themselves cancer causing agents, but are risk factors associated with the genesis of cancer, through professional exposures, behavior-related habits and addiction leading to exposure to recognized or suspected carcinogens. While lifestyle-related factors are usually well determined and thus accessible to epidemiological studies, cancer causing agents, because they are multiple, diverse and diffuse in the environment, are more difficult to identify and recognize and therefore evidence through classical epidemiological methods. Indeed, in the case of environmental carcinogens, we need to not only analyse the results of epidemiological studies, but also consider biological and toxicological data in close relationship with genetic susceptibility in the context of molecular gene–environment interactions, in order to interpret epidemiological studies in a more comprehensive way.

There are currently two opposite interpretations of the growing incidence of cancer. The first one considers that environmental pollutants can only make a minor contribution to the overall cancer incidence changes and therefore that increase in the size and ageing of the population, lifestyle influences such as smoking, alcohol consumption and diet, and new progress in diagnosis and screening procedures can explain most of the current increased cancer incidence [1], [2], [3]. Conversely, the second interpretation, considering that these arguments are not sufficient, estimates that in addition to these factors, there is a contribution from the environment and that involuntary exposure to diverse physical, chemical and biological agents, which may be present in the surroundings of individuals play a major role in the occurrence of the disease [4], [5], [6], [7], [8].

In a previous paper, we have shown that lifestyle-related factors, as well as ageing and new diagnostic and screening tests, cannot fully account for the overall recent growing incidence of cancer in the Western countries [9]. Moreover, we have proposed a hypothesis according to which the involuntary exposure to environmental carcinogens could contribute to the growing incidence of cancer in Western countries and, in a more recent paper, we have suggested that environmental carcinogens may in fact play a more important role in carcinogenesis than it is usually agreed [10].

In this paper, we intend to further show that studies of lifestyle-related factors are unsuccessful to fully understand the recent growing incidence of cancer and that cancer causing agents as evidenced from toxicological and biological investigations must be taken into account to interpretate correctly both carcinogenesis and current public health concerns.

Section snippets

Lifestyle-related factors

It is well agreed that smoking and to a lesser extent alcohol consumption, diet imbalance, obesity and lack of physical exercise can contribute to cancer in high-income countries.

Environmental causing cancer agents

In order to justify the hypothesis according to which the growing incidence of cancers could actually be related to environmental factors, we examine environmental carcinogens, in particular mutagens, and analyse their potential role in inducing cancers.

Conclusion

The industrial revolution over the second half of the last century and its consequences in domains such as energy, transport, agriculture, food and health led to synthesize, produce and introduce into the environment, millions of man-made chemicals or substances. As a result, according to the European commission, about 100,000 chemicals have been so far marketed, since the last world war, without sufficient toxicological control. Such products can act as persistent toxic pollutants and

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