Imagine if there were a drug that could reduce risk of cancer and cardiovascular disease by roughly 40%, without any adverse effects. Even better, people would only need to take it 2 or 3 times per week to obtain these preventive benefits.
It turns out there is such a thing. It’s called broccoli.
People who regularly eat broccoli once or twice weekly can reduce their all-cause mortality by an impressive 32% to 43%, according to a new analysis of data from more than 5,500 US adults.
Frequent broccoli consumption had a particularly strong impact on deaths from cancer and cardiovascular disease, according to a collaborative research team based at the Jilin University Hospital, Changchun, and the Beijing Shijitan Hospital, Capital Medical University, Beijing.
“Consuming broccoli 1–2 times per week for males and 3 or more times per week for females could significantly reduce all-cause mortality risk,” report Xiangliang Liu and co-authors. They suggest that, to a point, broccoli consumption may confer something like a “dose-response” effect on death rates from common diseases: the more frequently someone eats this healthful crucifer, the greater the mortality reduction.
They base that conclusion on a detailed study of data from 12,486 Americans in the NHANES (National Health and Nutrition Examination Survey) 2003-2006 cohort. The NHANES project uses an extensive Food Frequency Questionnaire (FFQ) to gather detailed dietary information from participants. The FFQ includes two questions specifically about broccoli: “Have you ever consumed broccoli?” and “How frequently do you consume broccoli?”
A total of 5,556 participants in the 2003-2006 NHANES cohort (2,743 males and 2,813 females) provided complete responses to these broccoli questions. All were over 20 years of age; 30% were over age 65.
Based on those responses, Dr. Liu and colleagues divided the cohort into four categories: never consumers (N=739), infrequent consumers who ate broccoli “less than once a week” (N=3,181), occasional consumers, defined as “1 to 2 times per week but less than 3 times per week” (N=1,216), and regular consumers, meaning those who ate broccoli “3 or more times per week” (N=420).
Impact on CVD & Cancer
During the 10-year follow-up period, which ended December 31, 2019, there were a total of 1,405 deaths from all causes among the 5,556 subjects (25.3%). Cardiovascular disease caused 504 deaths (35.9%), and cancer accounted for 292 deaths (20.7%). There were 107 deaths (7.6%) attributed to pulmonary/respiratory diseases, with the remainder attributed to accidents, renal disorders, diabetes, or “miscellaneous causes.”
After applying three different statistical models to control for a wide range of other variables associated with increased mortality, such as age, gender, race, education level, socioeconomic status, body mass index (BMI), smoking, and alcohol consumption, Liu and colleagues saw a clear signal: broccoli intake is inversely correlated with mortality.
In the statistical model with the strictest controls on potentially confounding variables, they found that compared with people who said they never ate broccoli, those who ate it occasionally (less than once weekly but several times per month) had an all-cause mortality hazard ratio of 0.7—a 30% risk reduction. For those who ate broccoli 1-2 times per week, the hazard ratio dropped to 0.58. That’s a 42% risk reduction.
But among the broccoli-lovers, who reported eating it 3 or more times per week, the hazard ratio was 0.72 compared with never-eaters, a finding that suggests the risk-reductive effect plateaus at a certain intake frequency, beyond which there’s no further gain.
Looking specifically at cardiovascular risk, they found a similar pattern: compared with never-eaters, those who ate broccoli occasionally had a 21% risk reduction, and those who ate it 1-2 times weekly had a 38% risk reduction.
The cancer data also showed this pattern: those who ate broccoli occasionally had a 30% lower risk of cancer-related mortality than the never-eaters. For those who ate it 1-2 times per week, the hazard ratio was reduced by 41%. Among the most frequent broccoli eaters, the risk was also reduced by 41% compared with non-eaters, again suggesting that the protective effect reaches a plateau (Liu X, et al. Front Nutr. 2008).
Dr. Liu and his colleagues saw a distinct gender-based difference in the pattern of risk-reduction: Males seem to obtain a greater benefit at lower consumption frequency than females. The latter need to eat broccoli at least 3 times per week to gain the all-cause mortality reduction that men get from once or twice weekly intake.
The reasons for this difference are not entirely clear, but the authors do offer a couple of speculations about it:
“On the one hand, the intake of fruits and vegetables is inherently higher in females’ diets, so they may need to eat broccoli more frequently to produce significant health effects. On the other hand, increased estrogen levels can promote the expression of glutathione peroxidase, enhancing the body’s antioxidant capacity, which may make females require higher amounts of antioxidant nutrients in broccoli.”
Putting it simply, women tend to have higher antioxidant intake along with higher inherent antioxidant capacity than men do. Therefore, to see an impact on mortality, women would need to eat substantially more broccoli than men.
A True Superfood
The risk reductions reported by Liu and colleagues are impressive in their magnitude, but they should not be entirely surprising: broccoli is an extremely fiber-rich and nutrient-dense vegetable. The authors cite a number of key nutrients within broccoli which likely play a role in its risk-mitigating effects:
- High levels of direct antioxidants such as vitamin C, carotenoids, and anthocyanins, that can quench oxygen-free radicals and mitigate oxidative stress.
- Sulfur-containing phytochemicals like glucosinolate, which inhibit the production and release of inflammatory mediators, and which also stimulate production of antioxidant enzymes.
- Sulforaphane, which promotes insulin signal transduction in the liver and in skeletal muscle, thus improving insulin sensitivity and regulating blood glucose.
- High levels of vitamin K1, a fat-soluble vitamin that promotes production of clotting factors while inhibiting the synthesis and secretion of cholesterol from the liver.
- A wealth of flavonoids that can scavenge free radicals and accelerate cholesterol breakdown.
- High levels of water-soluble mucilaginous fiber, that can prolong gastrointestinal transit time and improve digestion, bind bile acids, and slow the absorption of carbohydrates, thereby preventing post-prandial glucose and insulin surges.
- Rich in minerals, especially magnesium, which can reduce cholesterol absorption.
“Adequate intake of broccoli helps maintain the functionality of pancreatic beta cells, preventing insufficient insulin secretion due to pancreatic cell injury and thus stabilizing blood glucose regulation,” the authors stated. “By regulating glucose and lipid metabolism and enhancing insulin sensitivity, broccoli can reduce the risks of metabolic syndrome, type 2 diabetes, and cardiovascular diseases.”
To some degree, Dr. Liu’s team was able to quantify the anti-inflammatory effects of broccoli consumption. Using blood samples obtained from the NHANES participants, they measured monocyte, lymphocyte, platelet, and neutrophil counts, and found a clear reduction in the neutrophil-to-lymphocyte ratio—a key cellular marker of inflammation—associated with increased broccoli intake.
“Substantial evidence indicates that chronic inflammation and oxidative stress play important roles in the pathogenesis of various chronic diseases, including cancers, cardiovascular diseases, and type 2 diabetes,” Liu and colleagues state in their report. “Therefore, the abundant anti-inflammatory and antioxidant components in broccoli may be important nutritional mechanisms for its beneficial effects against chronic diseases.”
Who’s Eating Broccoli?
In their analysis, the Beijing researchers found several interesting demographic disparities in frequency of broccoli consumption within the NHANES cohort: women tended to eat it much more frequently than men, and non-Hispanic whites ate it more often than other racial/ethnic groups.
There was also a surprising relationship between socioeconomic status (as indicated by poverty income ratio) and broccoli consumption: those in the middle range tended to eat more broccoli than those at the low and the high ends of the socioeconomic spectrum.
Like any epidemiological study based on diet questionnaires and self-reporting, this one too has methodological limitations. The authors acknowledge the possibility of recall bias and participant subjectivity, which should be taken into consideration when drawing conclusions about the data.
Even with those limitations in mind, it is clear that regular broccoli consumption has a significant impact on reducing death rates from cardiometabolic and neoplastic disease. Pharmaceutical executives dream of finding novel drugs that can knock 30% or 40% off the mortality rates from common diseases.
Quantifying “Food as Medicine”
By studying the relationship between consumption frequency and disease-associated mortality rates, Liu and colleagues are, in a sense, attempting to quantify the concept of “food as medicine.”
They note that while there have been many studies of broccoli and other cruciferous vegetables over the decades, and most show positive health impacts. But few prospective studies have looked specifically at the effects of low, moderate, and high intake levels.
In the introduction to the study, they point out that “the available data do not provide specific recommendations for broccoli consumption frequency. Therefore, it is of great significance to use large sample prospective study results to analyze the dose–response relationship between broccoli intake frequency and all-cause and cause-specific mortality, which can provide guidance for dietary adjustment in different populations, especially dietary interventions for patients with chronic diseases.”
Though further research is needed, not just on broccoli, but on other ‘healthy’ vegetables, Liu’s study makes a strong case that men who eat broccoli once or twice weekly, and women who eat it three or more times per week, are doing themselves a great favor.