Based on their findings, the study authors say the health benefits of these vegetables may be at least partly a result of their anti-inflammatory effects. "Our group and others have found that consumption of fruits and vegetables, particularly cruciferous vegetables, was associated with lower total mortality and cardiovascular disease mortality – however, the potential mechanisms behind this association are not well understood," Dr Gong Yang told Reuters Health by email.
Yang is a researcher at Vanderbilt University Medical Centre in Nashville, Tennessee, and senior author of the study. "Chronic inflammation is implicated in the pathogenesis of cardiovascular and other chronic diseases – we therefore examined whether cruciferous vegetable intake may relate to inflammation," he said.
In animal studies, high intake of cruciferous vegetables or certain key compounds within them has been found to lower inflammation, Yang's team writes in the Journal of the Academy of Nutrition and Dietetics.
To see whether that is the case in people too, Yang and colleagues analysed signs of inflammation in the blood of 1 005 middle-aged Chinese women who filled out questionnaires about their diets as part of the Shanghai Women's Health Study.
The participants included in the new analysis were generally healthy, and had an average age of 58. Yang and his colleagues divided the women into five groups based on their daily intake of cruciferous vegetables.
The median intake of cruciferous vegetables was just under one cup per day, with women in the lowest fifth consuming about half that amount. The women in the top fifth of consumption took in about 1.5 cups of cruciferous vegetables every day.
The researchers then measured levels of signalling molecules involved in causing inflammation in the women's blood. Blood levels of three important inflammatory molecules – tumour necrosis factor-alpha (TNF-a), interleukin-1beta (IL-1b) and interleukin-6 (IL-6) were lowest among women with the highest intakes of cruciferous vegetables.
The women who consumed the most cruciferous vegetables had, on average, 13 % less TNF-a, 18% less IL-1b, and 25% less IL-6 than women who ate the fewest.
The researchers found a similar inverse relationship between the inflammation markers and intake of all vegetables combined, but not when they looked strictly at non-cruciferous vegetables. "Cruciferous vegetables may have health benefits through modulating inflammation," Yang said. "However, it is premature to make any dietary recommendation on the basis of this single observational study."
"It's an important message – we always hear people saying 'eat your vegetables', but it's also important to know that these aren't just theoretically good – we know that they really do have important health effects," Dr Neil Barnard told Reuters Health.
Barnard is president of the Physicians Committee for Responsible Medicine and an advocate of plant-based diets. Also an adjunct assistant professor of medicine at George Washington University, in the District of Columbia, Barnard was not involved in the new study.
Inflammation is thought to be part of a cycle that promotes heart disease, and heart disease in turn promotes more inflammation. "Bottom line, if you're eating a lot of cruciferous vegetables your health is better, and specifically, inflammation markers are diminished," he said. "That means you're going to have a healthier heart and you're going to live longer." Barnard added that cruciferous vegetables are good in other ways beyond reducing inflammation.
"They happen to be a source of a highly available calcium – the absorption of calcium from Brussels sprouts in something like 60%, whereas for milk it's only 30%," he said. "They also provide iron in a really good form, and provide a little protein." Barnard offered a couple of practical tips for consumers. "I think it's a good idea to cook cruciferous vegetables rather than just have them raw because they're more digestible that way," he said.
"Generally speaking, you can eat raw carrots and raw celery, but it's best to cook broccoli and cauliflower." He also suggests eating more than one serving of vegetables at a meal. "Instead of thinking about just one little modest vegetable serving at a meal, why not have two?" he said. "And a really great combination is green and orange, so you might have broccoli and sweet potato or you could have Brussels sprouts with carrots or cauliflower with carrots, something like that, so that you're mixing the colours."