Over the past decade or two, olive oil has received considerable attention from the nutritional community on account of its heart-healthy properties. The benefits this oil has for us have generally been ascribed to its high content of monounsaturated fat, which studies suggest effects changes in blood-fat levels that reduce the risk of cardiovascular complications, such as heart attack and stroke. However, another boost was given to olive oil's image recently when a study published in the Annals of Oncology showed that its most plentiful monounsaturated fat - oleic acid - has the ability to mute the effect of a common breast cancer gene.

While this recent research linking olive oil's chief constituent with protection from breast cancer is promising, it is actually only part of a body of evidence which suggests this foodstuff may help ward off the big C. Specifically, laboratory studies have identified that olive oil contains a range of compounds known as polyphenols that have what is known as 'antioxidant' activity. Through their ability to quench potentially damaging molecules known as 'free radicals' in the body, antioxidants are thought to offer some protection against chronic diseases like cancer.

While the Annals of Oncology study does help our understanding of the beneficial effects the constituents of olive oil may have in the body, it is not the first piece of research to link olive-oil consumption with a reduced risk of breast cancer. The results of several studies appear to show that relatively high consumers of olive oil have about a 25 per cent reduction in risk of breast cancer compared to low consumers. Other research has linked higher olive-oil consumption with a reduced risk of cancers of the ovary and womb. The cancer-quelling properties of olive oil seem to extend to men, too, with studies linking it to some protection from cancers of the colon, pancreas and lung. All this research has led some scientists to suggest that a decent intake of olive oil may help to explain the relatively low incidence of some cancers in the Mediterranean.

Those looking to get good doses of polyphenols from their olive oil are advised to opt for extra virgin varieties as lab analysis reveals that it is these oils that offer the highest polyphenol content. And it is not just olive oil but also olives that offer a rich stash of these nutrients. Tests show that black olives generally contain higher levels of polyphenols compared to green varieties. The preferred chemical constitution of black olives is reflected in enhanced antioxidant activity, too. Evidence suggests that olives and olive oil have the potential to protect against both heart disease and cancer.

Dear John

Some time ago I had a 'glucose tolerance test' which suggested I have type 2 diabetes. As a result, I made a conscious effort to be more active. My fasting blood sugar levels are now normal. Is it possible that I am no longer diabetic? When I asked the practice nurse if I could be re-tested she responded with disdain.
John Y

Diabetes is a condition characterised by higher-than-normal levels of sugar in the bloodstream. Type 2 diabetes generally comes on later in life, and is believed to be intimately related to diet and activity. My experience in practice is that, with appropriate lifestyle adjustment, this condition can be reversed in some people, particularly those for whom the condition is mild in form and has not been present very long. It is possible that your increased activity may have pushed you into a non-diabetic state. However, even if this is the case, it does seem as though you have a predisposition to diabetes. It may also help if you restrict consumption of refined sugar and starches that tend to disrupt blood sugar levels, such as bread, potatoes, rice, pasta and breakfast cereals.

Nutrition news

Vitamin D contributes to muscular function, and research has suggested that low levels of this nutrient may predispose to immobility in the elderly. In recent research published in The American Journal of Clinical Nutrition, the body levels of vitamin D were measured in more than 4,000 adults over the age of 60. Each of the study participants then underwent two standard tests of mobility. The researchers found that individuals with the highest levels of vitamin D in their bodies tended to be the most mobile, and the higher the level, the greater the mobility. This study provides further evidence that maintaining adequate levels of vitamin D in the body is important for maintaining mobility in the elderly.

Most of the body's vitamin D requirements are met through the action of sunlight on the skin. For some, the cold weather and shortened days can make winter a danger time for vitamin D deficiency. Spending at least half an hour outside each day will help reduce the risk of a shortfall in vitamin D, as can consuming vitamin D-rich oily fish or cod liver oil (at a dose of about 1 teaspoon a day).

· If you have any issues you would like Dr Briffa to address in his column, please email him on john.briffa@observer.co.uk. Please note that Dr Briffa cannot enter into any correspondence. You can also visit drbriffa.com. Before following any recommendations in this column, you should consult your own medical adviser about any medical problems or special health conditions