A diet rich in vegetables such as tomatoes, carrots and leafy vegetables, could cut the risk of adult asthma by about 20 per cent, says new research.
The "five-a-day" message is well known, but applying this does not seem to be filtering down into everyday life. Recent studies have shown that consumers in both Europe and the US are failing to meet recommendations from the WHO to eat 400 grams of fruit and vegetables a day.
The new study, from the Instituto Nacional de Salud Publica, Mexico, reports that women who ate a diet high in fruits and veg such as tomatoes, carrots and leafy vegetables considerably reduced their risk of asthma, a condition that affects 30 million people in Europe, and costs about €10 bn per year in lost productivity in Europe.
Published in the journal Thorax (Vol. 61, pp. 209-215), the researchers report the results of a prospective investigation of 68,535 women whose dietary habits were recorded as part of the French branch of the European Prospective Investigation into Cancer and Nutrition (EPIC).
Dietary intakes were measured from food frequency questionnaires of the daily intake of 208 food items.
After eleven years of follow-up, the researchers found that women who consumed more than 90 grams per day of leafy vegetables had a 22 per cent lower risk of asthma than those who ate less than 40 grams per day.
Similar risk reductions were also seen for tomatoes (20 per cent) and carrots (18 per cent).
The researchers also reported that women who used dietary supplements were more likely to be thinner, eat significantly more fruit and vegetables, but also more likely to report allergies.
The underlying mechanism or mechanisms of protection, say the scientists, is most probably due to the a combination and/or interaction of nutrients from the fruit and vegetables.
"One biological mechanism may be associated with the effect of antioxidant vitamins, such as carotenoids. Carrots and leafy vegetables are rich in carotenoids (alpha- and beta-carotene, lutein and zeaxanthin) which protect cells from oxidative stress.
Tomato juice, carrot juice and spinach powder have been shown to increase plasma levels of cystolic glutathione transferase [a family of enzymes that can play a role in the detoxification of lipid peroxidantion products], an effect attributed to carotenoids," wrote lead author Isabelle Romieu.
The researchers also noted that leafy vegetables are a rich source of folate, which has been linked to reduction in DNA damage due to oxidative stress.
The strengths of the study include the large number of prevalent asthma cases and the wide variability of the reported diets. However, the use of questionnaires did not permit the researchers to assess modifications of a woman's diet due to their asthma.
The study is yet more support for increasing the daily intake of fruit and vegetables - a recommendation that should be relatively easy to implement.
"Public health messages need to be simple and recommendations for food intake are easier to follow than recommended daily intakes of specific nutrients," said Romieu.
The findings have been welcomed by British charity Asthma UK, which said that the results supported the push for a diet rich in fruit and vegetables, but mentioned that further studies were needed.
A spokesperson for the charity told NutraIngredients.com: "There are a few studies which suggest that eating more of certain types of food can improve symptoms.
Research into increasing intake of Vitamin C, magnesium and fish oils (omega-3 fatty acids) have all shown benefits in some studies but no benefit in others. Further research is necessary before the link between diet and asthma is fully understood.
Asthma UK would encourage all people with asthma to strive towards general good health through eating a healthy diet made up of plenty of fruit and vegetables.
A report from the European Union showed that global fruit and vegetable production was over 1,230 million tonnes in 2001-2002, worth over $50 bn (€41 bn). Asia produced 61 per cent, while Europe and North/Central America both producing nine per cent.