In this meta-analysis, broccoli sprout supplementation was associated with significant reductions in SBP and DBP compared to the baseline. This finding is in agreement with the study of Mirmiran and colleagues, who reported moderate yet significant reductions in SBP (136 to 122 mmHg; P < 0.05) and DBP (89.8 to 80.4 mmHg; P < 0.05) following broccoli sprout administration in
H. pylori-infected patients (
21). Changes in blood pressure and endothelial function of hypertensive participants were primarily attributed to the age and gender of the population in another publication (
8). Few studies have discussed the anti-hypertensive properties of broccoli sprouts in human populations; however, investigations on spontaneously hypertensive stroke-prone rat models confirm the significant improvements in SBP, DBP, and inflammation status following broccoli sprout administration (
6). Detected changes were explained by the actions of glucoraphanin and sulforaphane through antioxidative properties (
26). It is believed that sulforaphane-induced upregulation of phase II enzymes could decrease the oxidative stress experienced by vascular smooth muscle cells. Also, sulforaphane increases existing contents of glutathione conjugation and subsequently alters activities of glutathione reductase and glutathione peroxidase; these changes are correlated with improved relaxation of the aorta and significantly decrease the blood pressure (
27).
This study found clinically significant reductions in HDL and LDL following dietary broccoli sprout intake (
Figures 4 and
5), which is partly consistent with the literature (
21). In a phase 1 study, 100 g/d of fresh broccoli sprouts improved the lipid metabolism of participants one week after the intervention (
9). Nevertheless, a 2014 clinical trial reported no significant changes in the TG and TG/ HDL levels following broccoli sprout administration (
21). Similarly, in a four-week clinical trial, hypertensive participants showed no significant changes in LDL, HDL, and TC levels (
8). The effect of broccoli sprout on lipid-related parameters was gender-specific in animal studies; the pattern of hypocholesterolemic changes varied between the male and female Syrian hamsters (
28), and acute administration of broccoli sprouts’ ethanol extracts only decreased the serum levels of TC, TG, LDL, and TG/ HDL in male rats fed on high-fat diets (
7). Reduced levels of fat absorption by the phytonutrient content (
29) and the inhibition of lipoprotein lipase activity in the adipose tissue (
7) may explain the mechanisms of changes in this context.
The potential health benefits of high sulforaphane-yielding broccoli sprouts are discussed in various clinical trials, animal studies, and in vitro models. Nevertheless, few human trials have focused primarily on cardiometabolic outcomes. Due to the lack of adequate data, as well as high levels of heterogeneity between the studies in terms of the intervention duration and dosage, and the health status of the participants, we could not detect any significant effects on glycemic, oxidative, and inflammation-related biomarkers. Meanwhile, existing literature suggests that adherence to a broccoli sprout-containing diet positively attenuates glycemic profiles and diabetic status. A double-blind clinical trial concluded that 5 g/day and 10 g/day of low sulforaphane-yielding sprout powder (0.4% compared with 1 - 2% in other studies) significantly decreased the blood glucose level (
11), which could be related to the anti-inflammatory properties of broccoli sprouts. The inhibitory effects of sulforaphane on the NF-κB pathway (
30) and the potential role of sulforaphane in the activation of peroxisome proliferator-activated receptors (PPARs) are among the other possible mechanisms (
31).
Anti-inflammatory properties of broccoli sprouts are key in the potential effects on the cardiometabolic health. Accordingly, Mirmiran and colleagues confirmed significant reductions in hs-CRP, IL-6, and TNF-α concentrations following broccoli sprout supplementation (
22). Broccoli sprouts are a potential inhibitor of proinflammatory cytokines production (
32). Sulforaphane could also act as an inhibitory factor in the expression of cyclooxygenase-2 and an inducible factor in lipopolysaccharide-stimulated nitric oxide synthase (
33), which all in all, limits the lipopolysaccharide-stimulated production of TNF-a and IL-1b in vitro (
6). Likewise, the antioxidative features of broccoli sprouts prevent the onset and progression of diverse micro and macro-vascular issues (
6,
34) by the potent induction of phase 2 antioxidant enzymes and reduction of oxidative species (
35). Acute supplementation with broccoli sprout is linked with a significant reduction in malondialdehyde, oxidized LDL, and oxidative stress index levels and an increase in total antioxidant capacity (
23). Also, daily consumption of fresh broccoli sprout is linked with the reduction of urinary 8-isoprostane and increase in the CoQ10H2/coenzyme Q10 ratio level among healthy individuals (
19). Therefore, incubating human microvascular endothelial cells with sulforaphane potentially can prevent mitochondrial dysfunction, trigger the formation of reactive oxygen species, and attenuate hyperglycemia-induced activation of hexosamine and protein kinase C (PKC) pathways and protein glycation under hyperglycemic conditions (
31).
To the best of our knowledge, this is the first systematic review and meta-analysis that exclusively focused on the cardiometabolic effects of broccoli sprouts. This research can pave the way for further studies of functional foods with an emphasis on cruciferous vegetables. Nevertheless, the high heterogeneity between the studies is among the limitations of this research, which can be explained by the varying doses and forms of broccoli sprout administration, sulforaphane yield of the supplements, and differences in the study populations and participants’ health status. Also, the low number of eligible studies, the lack of adequate data for subgroup analysis, and the broad inclusion criteria for the qualification of the studies may have increased the heterogeneity and challenged the application of final findings to other populations.