Researchers from the University of Leicester in the UK state that the benefits of the vegetables may be linked to their antioxidant content, with other observational studies highlighting the likes of beta-carotene, vitamin C, polyphenols and magnesium.
Writing in the British Medical Journal (BMJ), the researchers state, however, that the their results “support the evidence that ‘foods’ rather than isolated components such as antioxidants are beneficial for health”.
“The results support the growing body of evidence that lifestyle modification is an important factor in the prevention of type 2 diabetes,” wrote Professor Melanie Davies and her co-workers. “The potential for tailored advice on increasing intake of green leafy vegetables to reduce the risk of type 2 diabetes should be investigated further.”
Diabetes affects an estimated 24 million Americans, equal to 8 percent of the population. The total costs are thought to be as much as $174 billion, with $116 billion being direct costs from medication, according to 2005-2007 American Diabetes Association figures.
In an accompanying editorial in the BMJ, Professor Jim Mann from the University of Otago in New Zealand, and Dr Dagfinn Aune from Imperial College, London (UK), said that the findings are a useful reminder that giving dietary advice may be just as good, if not better, than prescribing drugs.
“Although it may be reasonable to draw attention to the potential benefits of green leafy vegetables, which could be incorporated as one of the five recommended portions of fruit and vegetables a day, we must be careful that the message of increasing overall fruit and vegetable intake is not lost in a plethora of magic bullets,” they added.
Professor Davies and her co-workers searched the literature and found six studies that met their criteria. The studies provided data for 223,512 people aged from 25 to 70. While no overall association was seen for the consumption of vegetables, fruit, or fruit and vegetables, a greater intake of green leafy vegetables was associated with a 14 percent lower risk of type-2 diabetes.
“Further investigation is warranted to understand the mechanisms involved in the proposed relation between green leafy vegetables and risk of type-2 diabetes,” added the researchers.
2010, 341:c4229, doi:10.1136/bmj.c4229
“Fruit and vegetable intake and incidence of type 2 diabetes mellitus: systematic review and meta-analysis”
Authors: P. Carter, L.J. Gray, J. Troughton, K. Khunti, M.J. Davies