Almost a fifth of all ill health in poor countries and millions of deaths can be attributed to environmental factors, including climate change and pollution, according to a report from the World Bank.

Unsafe water, poor sanitation and hygiene as well as indoor and outdoor air pollution are all said to be killing people and preventing economic development. In addition, says the bank, increasing soil pollution, pesticides, hazardous waste and chemicals in food are significantly affecting health and economies.

More controversially, the report, released yesterday in New York, links cancers to environmental conditions and says global warming has a major impact on health. "For almost all forms of cancer, the risk of contracting this disease can be reduced if physical environments are safe for human habitation and food items are safe for consumption," says the report.

It also cites the spread of malaria and dengue fever as climate change intensifies. Global warming, says the report, is leading to lower yields of some crops and the salination of coastal areas.

"In 2000 more than 150,000 premature deaths were attributed to various climate change impacts, according to the World Health Organisation," it says.

While tobacco, alcohol and unsafe sex are still the most likely threats to health in developing countries, rapid urbanisation and the spread of slum conditions are now major hazards, says the report.

"Some 1.1 billion people lack access to safe water and 2.6 billion lack access to safe sanitation. [This leads to] about 4 billion cases of diarrhoea a year, which cause 1.8 million deaths a year, mostly among children under five," it says.

Sanitation, says the bank, which is committed to increasing spending on the environment, is very much "a forgotten problem", with spending on improvements estimated at just $1bn in 2000 - less than 10% of that spent on water.

Millions of people who have moved to cities to find work have swapped indoor for outdoor air pollution, suggests the report. Urban air pollution is estimated to cause about 800,000 premature deaths, it says, approaching the number of people affected by indoor air pollution from wood fires in poorly ventilated homes in rural areas.

According to the report, which uses WHO statistics, high concentrations of minute particles released by smoky fires are now responsible for over 1.6 million deaths a year. Acute respiratory infection, largely caused by indoor air pollution, it says, was responsible for 36% of all registered infant deaths in Guatemala between 1997 and 2000.

The report also says manmade chemicals such as pesticides have an increasing impact on the health of poor people.

A survey of child labour in several developing countries, it says, found more than 60% of all working children were exposed to hazardous conditions, and more than 25% of these hazards were due to exposure to chemicals

"Without a healthy, productive labour force, we will not have the economic growth that is necessary to ensure a pathway out of poverty. Poor people are the first to suffer from a polluted environment," said Warren Evans, director of the bank's environment department.