If you are afraid of HIV, malaria, cancer or obesity induced diseases, you'd better find out what's the direct or indirect human killer worldwide: water, air and soil pollution. 40% of humans are exterminated by it.

"Such environmental degradation, coupled with the growth in world population, are major causes behind the rapid increase in human diseases, which the World Health Organization has recently reported. Both factors contribute to the malnourishment and disease susceptibility of 3.7 billion people," said David Pimentel, Cornell professor of ecology and agricultural sciences.

His team made a meta-analysis of over 120 researches on the effects of population growth, malnutrition and environmental degradation, all connected to human diseases. "We have serious environmental resource problems of water, land and energy, and these are now coming to bear on food production, malnutrition and the incidence of diseases. Of the world population of about 6.5 billion, 57 % is malnourished, compared with 20 % of a world population of 2.5 billion in 1950," said Pimentel.

Malnutrition kills directly 6 million children annually, but what's even worse is that the survivors are more vulnerable to potentially deadly germs like acute respiratory infections, malaria and others.

About 50 % of the world's population is crowded into urban areas, often lacking proper sanitation, fact that renders them vulnerable to epidemics, like measles and flu. As 1.2 billion people do not have access to clean water, waterborne infections represent 80 % of the total. Water pollution boosts the populations of malaria-carrying mosquitoes, and the parasite kills 1.2-2.7 million people annually, 90% African children.

Air contamination (smoke and toxic chemicals) kills 3 million people annually, while the lack of hygiene provokes 5 million deaths each year, over 50 % being children. US alone damp approximately 3 million tons of toxic chemicals into the air annually, products that induce cancer, birth defects, immune system impairment and other severe health problems.

Soil is loaded with toxic chemicals and germs, which enter the human body through direct contact, food or water. The increasing oil erosion just spreads worldwide the pathogens.

The number of germs getting drug-resistance is increasing, and global warming, combined with lower biological diversity boosts the parasites' abilities to colonize new territories. That's why diseases thought under control, like tuberculosis and influenza, are re-gaining terrain, while new dangers, like bird flue, SARS, West Nile virus and Lyme disease, have emerged.

"A growing number of people lack basic needs, like pure water and ample food. They become more susceptible to diseases driven by malnourishment, and air, water and soil pollutants. Relying on increasing diseases and malnutrition to limit human numbers in the world diminishes the quality of life for all humans and is a high-risk policy," warned Pimentel.