Cruciferous vegetables like broccoli reduce blood pressure compared to root and squash vegetables

By Pooja Toshniwal PahariaReviewed by Danielle Ellis, B.Sc.Sep 10 2024

Daily consumption of four servings of cruciferous vegetables over a 2-week period resulted in reduced blood pressure in middle-aged and older adults with mildly elevated blood pressure compared with root and squash vegetables

In a recent study published in BMC Medicine, researchers performed a crossover-design randomized controlled trial (RCT) to explore the influence of cruciferous vegetable consumption on blood pressure (BP) among adults with mild hypertension in Australia.

Background

High blood pressure is a primary risk factor for cardiovascular disease. Cruciferous vegetables can lower animal blood pressure, but evidence in humans is limited. Their cardiovascular health benefits include improved endothelial function, reduced glycemic complications, and reduced atherosclerotic plaque development and progression. Cruciferous vegetables also contain vitamin C, nitrate, magnesium, vitamin K, folate, and flavonoids that influence blood pressure.

Observational studies and meta-analyses report that increased cruciferous vegetable consumption lowers cardiovascular illness risk. Objective biomarkers of cruciferous vegetable consumption as urinary thiocyanate yielded similar results. However, the mechanisms by which cruciferous vegetables benefit cardiovascular health are unclear.

About the study

The RCT investigated whether consuming cruciferous vegetables regularly could lower brachial systolic BP (SBP) among mildly hypertensive Australian adults.

The VEgetableS for vaScular hEaLth (VESSEL) study recruited individuals aged 50 to 75 years from August 2019 to March 2021. Participant SBP values ranged from 120 to 160 mm of Hg, with diastolic BP below 100 mm Hg. They completed the Dietary Questionnaire for Epidemiological Studies (DQES) to assess baseline dietary intake.

The researchers randomized the study participants to receive 14-day dietary interventions with a washout period of 14 days. They compared cruciferous vegetables (active intervention, four servings, 300 g daily) to squash and root vegetables (control, four servings, 300 g daily) consumed as soups during meals. The active soup comprised 10% kale, 25% cabbage, 25% cauliflower, and 40% broccoli. The control soup comprised 10% sweet potato, 20% carrot, 30% pumpkin, and 40% potato.

Diet diaries and biological markers such as serum and urine S-methyl cysteine sulfoxide (SMCSO) and serum carotenoids assessed dietary adherence. High-performance liquid chromatography (HPLC) with tandem mass spectrometry assessed biomarker levels. The primary study outcome was 24-hour brachial SBP. Secondary outcomes included arterial stiffness, oxidative stress, and inflammation.

BP monitors took readings every 20 minutes during the day (6 am to 10 pm) and every 30 minutes at night (10 pm to 6 am). The aortic augmentation index (AIx) indicated ambulatory arterial stiffness. Researchers measured height, weight, body mass index (BMI), waist circumference, hip circumference, and fat mass before and after intervention. The Community Healthy Activities Model Program for Seniors (CHAMPS) evaluated physical activity, and the Perceived Stress Scale (PSS) assessed stress.

Enzyme-linked immunosorbent assays (ELISA) analyzed serum high-sensitivity interleukin-6 (hsIL-6) levels to measure inflammation. Investigations included urinary and serological levels of sodium, potassium, and creatinine. In addition, researchers measured serological triglycerides, glucose, high-density lipoprotein (HDL), low-density lipoprotein (LDL), total cholesterol, and high-sensitivity C-reactive protein (hs-CRP). Linear-type mixed-effects regressions evaluated SBP differences before and after intervention. The study excluded individuals with more than 20% of their measures missing or who spent more than four hours without taking their BP readings.

Results and discussion

The study included 18 individuals with a median age of 68 years; 16 were female, their BMI varied from 21 to 35 kg/m2, and their mean SBP was 136 mm Hg. Most participants (94%) were Caucasian, and 72% completely adhered to the intervention. The median daily consumption of cruciferous vegetables was 26 g. SMCSO and carotenoid levels significantly differed between the groups (active versus control mean difference: SMCSO: 23 mg per mL; carotenoids: −0.97 mg per mL).

The 24-hour brachial systolic BP values significantly reduced after the active intervention versus control (a 2.5 mm Hg-mean difference). Pre- and post-intervention SBP values in the active group were 126.8 mm Hg and 124.4 mm Hg, respectively. The corresponding values in the control groups were 125.5 and 124.8 mm of Hg, respectively. Daytime SBP drove the changes, with a mean reduction of 3.60 mm Hg.

Serum triglyceride levels significantly reduced after the intervention (active versus control, a 0.20 mmol per L-mean difference). The improvements in SBP seen with the intervention were independent of weight reduction and dietary intake of sodium and potassium. The active intervention significantly increased serum sulforaphane, suggesting that glucosinolates, specifically glucoraphanin, may reduce BP. These compounds increase nuclear factor erythroid 2-related factor 2 (Nrf2) activity and inhibit nuclear factor kappa B (NF-ĸB) pathways. They may also act as hydrogen sulfide (H2S) donors to induce vasodilation.

The study showed that consuming cruciferous vegetables daily for two weeks reduced systolic BP compared to squash and root vegetables among mildly hypertensive adults. Combining these results with previous meta-analyses indicates that the 2.5 mmHg reduction in SBP resulting from increased cruciferous vegetable consumption in this study could reduce the risk of major cardiovascular events by 5.0%. Future research should explore the impact of targeted cruciferous vegetable consumption on population health, considering more diverse populations for greater generalizability.