A lot of people in the world can not enjoy good health because of the social environment where they are born, live, grow, work and age, the World Health Organization (WHO) said in a report on Thursday.

Biology does not explain why a girl in Lesotho is likely to live 42 years less than another in Japan, and why the risk of a woman dying during pregnancy and childbirth is 1 in 17,400 in Sweden, while in Afghanistan the odds are 1 in 8, according to the report.

Instead, those health inequities result from the different social environments, or "social determinants of health", said the report, which was completed after three years of investigation by the WHO's Commission on the Social Determinants of Health.

"(The) toxic combination of bad policies, economics, and politics is, in large measure responsible for the fact that a majority of people in the world do not enjoy the good health that is biologically possible," said the report.

"Social injustice is killing people on a grand scale," it said.

"Health inequity really is a matter of life and death," said Margaret Chan on Thursday in new report.

"But health systems will not naturally gravitate towards equity. Unprecedented leadership is needed that compels all actors, including those beyond the health sector, to examine their impact on health," she said.

She added that primary health care, which integrates health in all of government's policies, was the best framework for realizing health equity.

According to the report, health inequities -- unfair, unjust and avoidable causes of ill health -- not only exist between countries but within countries as well.

In general the poor are worse off than those less deprived, and the less deprived are in turn worse than those with average incomes.

This slope linking income and health is seen everywhere -- not just in developing countries, but all countries, including the richest. The slope may be more or less steep in different countries, but the phenomenon is universal.

Much of the work to redress health inequities lies beyond the health sector, the report said.

For example, water-borne diseases are not caused by a lack of antibiotics but by dirty water, and by the political, social, and economic forces that fail to make clean water available to all.

And heart disease is caused not by a lack of coronary care units but by lives people lead, which are shaped by the environments in which they live.

"We rely too much on medical interventions as a way of increasing life expectancy," said Michael Marmot, chairman of the WHO Commission on the Social Determinants of Health.

"A more effective way of increasing life expectancy and improving health would be for every government policy and program to be assessed for its impact on health and health equity; to make health and health equity a marker for government performance," he said.