New life expectancy figures show Americans some way behind countries like Canada, the UK and Australia. Why?

Living in the world's richest country comes at a price, and it's measured in life years.

Men in the US are on average aged 75 when they die. That is 1.5 years younger than men in the UK and 3.5 years younger than men in Australia, says a new study.

American women live on average to just under 81 - about three years younger than the average Australian woman.

While life expectancy in the US continues to improve, says the report by researchers at University of Washington in Seattle and Imperial College, London, it is not increasing as quickly as in other Western countries, so the gap is widening.

"The researchers suggest that the relatively low life expectancies in the US cannot be explained by the size of the nation, racial diversity, or economics," says the document, which ranks the US 38th in the world for life expectancy overall.

"Instead, the authors point to high rates of obesity, tobacco use and other preventable risk factors for an early death as the leading drivers of the gap between the US and other nations."

Risk factors smoking

obesity

high blood pressure

high low-density lipoprotein cholesterol

high dietary trans fatty acids

high salt intake

low dietary omega 3 fatty acids

high blood glucose

low intake of fruits and vegetables

alcohol abuse

physical inactivity Source: University of Washington

"We weren't surprised that we had lower life expectancies than other countries, but we were surprised by the fact that we were falling further behind," says Dr Ali Mokdad, professor of global health at the Institute for Health Metrics and Evaluation at the University of Washington.

Take a country like Australia, he says. "It also has a nation of immigrants. It also is a relatively young country. It has similar socioeconomic characteristics.

"It has an obesity problem, and yet it has continued to improve in life expectancy and remains one of the healthiest nations in the world."

So how should the US address these risk factors?

Smoking alone is responsible for one out of every five deaths in the US, the professor says, yet the US has not been as tough as Australia in restricting tobacco advertising and public smoking.

Australia also has a greater focus on primary care - which helps with health education, and early treatment of any problems - and it has done a good job reducing the number of road traffic accidents, he adds.

The US could also save 100,000 lives a year by reducing salt in people's diets, since high blood pressure kills one in six people, Dr Mokdad says.

Snapshot from Mississippi "We have high rates of poverty and high rates of uninsured or people lacking access to care. We have fewer primary care providers and fewer physicians per person than most states. And high rates of low education. "We have the highest rate of obesity in the country and therefore one of the highest rates of diabetes. A relatively high rate of tobacco use and high rates of cardiovascular disease, stroke and cancer. "It's going to take a long time to make progress, but we have 40 communities that have banned indoor smoking in public buildings, and the percentage of high school smokers is falling. In other ways, we are making being healthy an easier choice." Dr Mary Currier, Mississippi health officer

Then there's the big issue - about one in three adults is classified as obese. That's about 10 times as many as in long-living countries like Japan, according to OECD figures.

But the US is a big country, and while parts of Mississippi have a male life expectancy of 67, behind nations like the Philippines, women in areas of Florida live as long, on average, as the Japanese, who top the longevity rankings.

It is precisely this kind of inequality that goes some way to explain why the US - and the UK to a lesser degree - lag behind other countries, according to Danny Dorling, a professor of human geography at the University of Sheffield in the UK.

He believes a more even distribution of wealth, even if the average were lower, could mean longer lives for everyone.

"I think stress is a part of it - this is the key thesis of Michael Marmot and his book on the status syndrome. People get worn out faster with greater inequality.

"However there is much more. If you have most health spending just going on a few people who have the best health to begin with - [as in] the US system - that is hardly efficient.

"In a more unequal rich country more doctors are working on things like plastic surgery. More dentists whiten teeth than fix bad teeth and so on."

Infant deaths

While it is not surprising that poor Americans lose out from inequality, Prof Dorling argues that the rich may suffer too.

Image caption Several of the world's oldest people have been from Japan

"Top income groups are badly affected because their doctors are not necessarily mainly interested in their health but work for organisations that have to make an income," he says.

"I am not suggesting it is deliberate but you make more money out of a patient who spends more on many drugs and investigatory operations than one who lives longer with less intervention.

"In a more equal system the rich who are well get less intervention - and they live longer in the UK than the US."

Growing income inequality in the UK, since the 1970s, has has helped to push it down the European life expectancy rankings, says Mr Dorling.

However, life expectancy is not just about forecasts made for newborn babies.

When you look at life expectancy at 65 or 75, the US performs rather well, says Svetlana Ukraintseva, senior investigator at the Center for Population Health and Aging (CPHA) at Duke University in North Carolina.

Elderly Americans have a higher chance of surviving heart disease and many cancers than their counterparts in other rich countries, she says. Where the US lags behind is what happens at a much younger age.

"It's likely not the quality of medical care itself that is the problem but access to it. Medical insurance for all might help."

This is one goal of the healthcare reform signed into law in March 2010, which will oblige American adults to have health insurance when it comes into force in 2014.

However, this remains a controversial idea in the US and the legislation could yet come unstuck.

Challenges to the constitutionality of the law are working their way through the courts, and fierce opponents in the Republican Party make no secret of their desire to repeal the legislation if the opportunity arises.