PARIS • Soaring birth rates in developing nations are fuelling a global baby boom while women in dozens of richer countries are not having enough children to maintain population levels there, according to figures released yesterday.

A global overview of birth, death and disease rates evaluating thousands of data sets on a country-by-country basis also found that heart disease is now the single leading cause of death worldwide.

The Institute for Health Metrics and Evaluation, set up at the University of Washington by the Bill and Melinda Gates Foundation, used more than 8,000 data sources to compile one of the most detailed looks at global public health.

Their sources included in-country investigations, social media and open-source material.

It found that while the world's population rose from 2.6 billion in 1950 to 7.6 billion last year, that growth was deeply uneven according to region and income.

Ninety-one nations, mainly in Europe and North and South America, were not producing enough children to sustain their current populations, while fertility rates continued to grow in Africa and Asia.

Professor of Health Metrics Sciences Ali Mokdad, at the Institute for Health Metrics and Evaluation, said the single most important factor in determining population growth was education.

"It is down to socioeconomic factors but it's a function of a woman's education," he said. "The more a woman is educated... (the longer) she is delaying her pregnancies and so will have fewer babies."

Cyprus was the least fertile nation on earth, with the average woman giving birth just once in her life. In contrast, women in Afghanistan, Chad and Mali have on average more than six babies.

The United Nations predicts there will be more than 10 billion humans by the middle of the century. This raises the question of how many people the earth can support.

Prof Mokdad said that while populations in developing nations continue to rise, their economies are also growing. "Countries are expected to fare better economically and it's more likely that fertility there will decline and level out."

The study, published in The Lancet medical journal, also found that male life expectancy had risen to 71 years from 48 in 1950, while women are now expected to live to 76, compared with 53 in 1950.

The Institute for Health Metrics and Evaluation said heart disease is now the leading cause of death globally. "You see less mortality from infectious diseases as countries get richer, but also more disability as people are living longer," said Prof Mokdad.

"There are certain behaviours that are leading to an increase in cardiovascular diseases and cancer. Obesity is No. 1 - it is increasing every year."

AGENCE FRANCE-PRESSE