CHRONIC ILLNESSES CITED AS TOP THREAT BY 2020.

Byline: Shankar Vedantam Knight-Ridder Newspapers

A major new international health study reverses the recent flood of warnings about infectious diseases and predicts the biggest problems of the next quarter-century are likely to be chronic conditions, especially those that largely affect the elderly.

What this means, say the authors of the study, released Sunday by the World Health Organization and the World Bank, is that governments are spending too many of their health dollars on diseases like AIDS, and too few on mental illness, heart disease and cancer.

By 2020, tobacco-related disease will become the world's greatest killer, causing one in every 10 deaths, the study says. Those diseases claimed 3 million lives in 1990 - and they are expected to claim 8.4 million lives in 2020.

``If past trends are anything to go by, the mortality caused by infectious diseases will decline,'' said Christopher Murray, professor of health economics at Harvard University and the study's chief author.

The study argues that as the world's population ages - and wealth, education and medical technology spreads - doctors will increasingly be confronted with the diseases and problems of the elderly.

Infectious diseases, which wreak the greatest havoc among children, the poor and the uneducated, will remain dangerous and unpredictable foes, but deaths caused by these diseases in 2020 are expected to be about 10 million, down from 17.2 million in 1990.

Despite the expected drop, Anthony Fauci, the government's top infectious diseases scientist, said, ``We must be very careful we don't make the mistakes we made two decades ago when people felt we no longer had a problem with infectious diseases. If you look at the statistics, infectious diseases are still the leading cause of death in the world and third-largest cause of death in the U.S.''

The aging of the world's population, Murray said, ``has the tendency to shift disease toward noncommunicable conditions and injuries.''

What this means, say the study's authors, is that health dollars should be reallocated to prepare for the onslaught of chronic conditions - which are often expensive to treat and require long-term care - but which can also be headed off by promoting healthy lifestyles.

``A lot of people confuse aging with these diseases,'' said Richard Suzman, chief demographer at the federal government's National Institute on Aging. ``But again and again, we've found that many of them are preventable.''

A surprising finding of the study was that, measured by the disability caused, mental illnesses - led by major depression - will be the second-worst scourge by 2020, trailing only heart disease.

Mental illnesses are among the hardest to prevent - and to cure.

``We're learning that many mental illnesses are chronic recurring conditions and their treatment requires long treatment and maintenance,'' said Barry Lebowitz, the government's top scientist studying the mental illnesses of the elderly.

``The challenge in mental health care is not in making people well but keeping them well,'' he said.