Elsewhere, the growth potential is even greater. Starting from a low base of around $600 per capita in the world outside the US, spending is forecast to grow at rates of up to 15pc a year in the developing world. In many economies, health care spending is growing much faster than the GDP.

There are three drivers of this growth. First, the world is ageing fast which increases the incidence of age-related diseases such as many cancers and Alzheimers disease. Endologix, a heart disease specialist, has been doubling sales for the past five years and, with only 10pc of the US market in its focus area of aortic aneurysms, it has plenty of scope for further expansion.

Second, sedentary lifestyles are causing growth in a range of chronic diseases. Diabetes is an increasing problem as waistlines expand. A major beneficiary is Novo Nordisk, a global leader in insulin production with a 50pc share of the fast-absorbing variety. Third, demand for better health care is growing in emerging markets as incomes increase and life expectancy rises. Chinas pharmaceuticals market, for example, was already the eighth largest in the world in 2006 and is predicted to be the third biggest by the end of this year.

Apollo Hospitals, the worlds largest private hospital operator, has plans to expand the number of its sites in India by more than 50pc in the next five years.

One of the reasons why health care is so interesting to investors, apart from the scale of its growth, is the sectors diversity. That means it can appeal to different styles of investor, with big, cash-rich pharmaceuticals firms offering secure dividends, mid-sized health care companies offering growth prospects and biotech start-ups offering high risk, high return potential and the chance of a takeover.

Big pharmaceutical companies routinely use acquisitions to fill in products or skills where they dont have the right expertise. Many of the sub-sectors within health care march to very different beats, which makes it easier to smooth returns while different parts of the supply chain from manufacturing to marketing, will be in favour at different points in the cycle.

Big companies might fare better in a downturn while small-caps offer growth when markets are rising fast.

There arent many things that are certain in todays world but population growth and ageing are two about which we need have no doubts. The expansion of the emerging worlds middle class looks unstoppable too, and the combination of all three means that increasing demand for health care is as close to a given as investors can hope for however dreary the IMFs outlook.

Tom Stevenson is an investment director at Fidelity Worldwide Investment. The views expressed are his own.

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