In recent years, reports of the benefits of aspirin have increased, including modest reductions in the polyps that can lead to colon cancer.

Now, University of Minnesota researchers report an apparent association between taking aspirin and reducing rates of often-deadly pancreatic cancer by as much as 43 per cent. "This is an intriguing study, more along the lines of hypothesis as opposed to testing," said Dr Ernest Hawk of the National Cancer Institute. "I think that aspirin may very well have this sort of activity but I wouldn’t consider it definitive," he said. "They will have to work out the risks and benefits." Hawk noted that this was only an observational study, not a randomised, controlled trial. "It provides information that needs to be tested in a controlled study," he said. There have been prior studies of pancreatic cancer that didn’t see any statistical effect in aspirin use, Hawk added. Because aspirin can also have side effects, he said that people may not want to run out and start taking it just on the basis of this study, though "researchers may want to run out and do more studies."

Scientists have identified a hormone that caused the sensation every dieter craves : the feeling of fullness. The hormone, Peptide YY3-36 or PYY, is made by cells in the small intestine in response to food and then circulates to the brain, where it switches off the urge to eat.

"It stops you feeling hungry", said Stephen Bloom, a professor of endocrinology in London, who led a study of the hormone that was published in the journal Nature. "It controls you and me after every meal we eat."

PYY has been known since the 1980s, but its ability to suppress appetite was discovered only within the past years or so, Bloom said. In his study, people who were given a tiny dose of the hormone and offered a buffet lunch two hours later consumed about 33 per cent fewer calories than they did when they were not taking the hormone. They reported feeling full, but not overstuffed or ill. The effects lasted about 12 hours, and when the hormone wore off, the people had no tendency to overeat to make up for the calories they had missed.

Bloom said he hoped it would be possible to use PYY itself, a drug based on it or a diet that stimulates the body to make more PYY to help people lose weight. High fibre diets seem to stimulate PYY production naturally, he said. Pure PYY would have to be injected; it cannot be taken by mouth because it would be broken down in the stomach. But a drug based on PYY might be made in pill form.

The research is in its early stages. the study included only 12 people, none of them obese. Far more testing is needed to find out whether PYY or related molecules are safe and effective, especially for long-term use.

Another appetite suppresant, leptin, made by the body’s fat cells and thought to have promise in treating obesity, has turned out not to work because most overweight people are resistant to it.

A five mile wide ball of uranium and plutonimum acting like a giant nuclear reactor at the centre of the Earth is the source of the energy that sustains life, according to controversial new research.

The natural reactor generates the Earth’s magnetic shield, which protects the planet from bombardment by deadly particles from the Sun. It also provides the energy that powers volcanoes and the movement of continental plates.

If true, the theory would overturn current ideas of what lies at the heart of our planet. They suggest the Earth’s core contains a huge ball of solidified iron and nickel surrounded by a molten mantle. The new theory would also bring the Earth’s life to an end far earlier than previously forecast. Instead of lasting up to four billion years, the planet will die in just two billion years as the reactor runs out of fuel, cools and the protective magnetic shield is dissipated.

The study, by scientists at the US Department of Energy’s Oak Ridge Laboratory, looked at the radioactive elements given off during volcanic eruptions. They also designed a sophisticated computer model of how a reactor at the Earth’s core might behave.

"We found strong evidence that 4,000 miles beneath our feet the Earth’s core contains a fast-neutron breeder reactor made of uranium and plutonium, a type that can regenerate new fuel for itself. What’s more, such a reactor would have a life similar to that of the Earth," said Marvin Herndon, the Oak Ridge researcher who presented the findings at a recent conference of the American Geophysical Union.

The researchers believe the five-mile-wide ball of uranium has been operating as a nuclear reactor for about 4.5 billion years with an output of about 4 m megawatts.