The idea that old studies cannot generate new results and do not therefore warrant funding, is belied by findings from long-term epidemiological studies. How else could we know that men on Crete live six years longer than those living in Zutphen because of differences in diet and lifestyle? Or that eating fatty fish at least once a week helps to prevent heart attacks? These and other points were raised by Daan Kromhout on 16 April, during his official farewell address as Professor of Public Health Research at Wageningen University.
Professor Daan Kromhout has studied the impact of diet and lifestyle on the development and prevention of cardiovascular disease since the start of his academic career. In his farewell address entitled Of fats and foods, he summed up the main results of the research he has led in this field over several decades. When he was appointed as a professor 30 years ago, Kromhout hoped to be able to prove that diet and lifestyle are decisive factors in the development of cardiovascular disease. He now admits that he has only partly succeeded. There is no firm proof that omega-3 fatty acids from fatty fish protect people from cardiovascular disease. Research to ascertain whether flavonoids play a protective role against cardiovascular disease is still in the early stages, and the same is true of dietary habits. So, Kromhout argues, despite the opposition and lack of funding, that epidemiological studies are still essential and must be continued.
Seven Countries Study
In 1978, Daan Kromhout was appointed as lead researcher in the Zutphen Study in the Netherlands. The study involved monitoring hundreds of male inhabitants of Zutphen from 1960 onwards, documenting their diets, lifestyles and health, particularly with regard to cardiovascular disease. He was also one of the leading figures in the Seven Countries Study, in which similar studies were carried out in the USA, Finland, Italy, former Yugoslavia, Greece and Japan. The Seven Countries Study, which has been running for more than fifty years, has generated a wealth of information about the causes of cardiovascular disease (ten books and more than 500 publications). (See: www.sevencountriesstudy.com)
In a nutshell, the study showed that cholesterol in the blood, blood pressure and diabetes, along with diet, physical activity, smoking and alcohol are all important factors in predicting cardiovascular disease.
Alpha Omega Trial
In 2010, the results of the Alpha Omega Trial were published. This was the first, double-blind dietary intervention study into the effects of omega-3 fatty acids on cardiovascular disease. Almost 5,000 heart patients from 32 Dutch hospitals took part. Kromhout led the study, in which additional amounts of omega-3 fatty acids in margarines were compared to a placebo margarine. The study failed to show any health benefits from the 'healthy' omega-3 fatty acids. In his farewell address, Kromhout concluded that 30 years of research into the link among fish, omega-3 fatty acids and fatal heart disease had taught him that eating fatty fish once a week lowers the risk of fatal heart disease in healthy adults, but that adding omega-3 fatty acids to the diet of heart patients receiving adequate drug treatments does not reduce their future cardiovascular disease risk.
Another field examined closely by Kromhout et al. for more than 25 years is that of flavonoids and cardiovascular disease. Flavonoids occur naturally in plant foods such as tea, chocolate and apples. A recent intervention study showed that the flavonoid epicatechin has a positive effect on cardiovascular risk factors. But, says Kromhout, although the research into flavonoids is promising, it is still at an early stage.
Diet and lifestyle
According to Professor Kromhout, the Zutphen Study and the Seven Countries Study showed that in the 1960s the traditional Mediterranean diet pattern consisted of lots of olive oil, wholemeal bread, vegetables, fruit, pulses, as well as some fish and not too much red meat and dairy products, is not only good for cardiovascular disease, but also for all causes of death together. The risks were higher in the north of Europe (Finland and the Netherlands), where the typical 1960s diet comprised more full-fat milk, butter, hard margarine, meat and sugar. Over the last 50 years, the average age at death of Cretans was 81.6 years, which according to Kromhout is dramatically higher than that of men from Zutphen at 75.9 years. But diet is not the only factor that affects healthy ageing, he says. Not smoking, getting enough physical activity and moderate alcohol consumption all help to improve the quality and quantity of life.