The authors argue that "our results support the evidence that 'foods' rather than isolated components such as antioxidants are beneficial for health - results from several supplement trials have produced disappointing results for prevention of disease."

In conclusion, they believe that offering tailored advice to encourage individuals to eat more green leafy vegetables should be investigated further.

In an accompanying editorial, Professor Jim Mann from the University of Otago in New Zealand, and Research Assistant Dagfinn Aune from Imperial College London, are cautious about the results and say the message of increasing overall fruit and vegetable intake must not be lost "in a plethora of magic bullets," even though green leafy vegetables clearly can be included as one of the five portions of fruit and vegetables per day.

They argue that given the limited number of studies, "it may be too early to dismiss a small reduction in risk for overall fruit and vegetable intake or other specific types of fruits and vegetables and too early for a conclusion regarding green leafy vegetables."

Source: BMJ-British Medical Journal