Research
Hundreds of research studies occur every year on the cancer preventive potential of plant nutrients. The cancer preventive property of cruciferous vegetables and sulforaphane is the subject of over 700 research studies to date. The following table is a representation of the epidemiological evidence of cancer prevention by cruciferous vegetables.
Epidemiological Evidence of Cancer Prevention by Cruciferous Vegetables
| Site of cancer | Amount of crucifers eaten | RR - relative risk OR-odds ratio (P value) |
Reference |
|---|---|---|---|
| Bladder | >5 servings/week | RR 0.49 (0.008) | Michaud et al. (1999) |
| Lymphoma | >5 servings/week | RR 0.67 (0.03) | Zhang et al. (2000) |
| Prostate | 5 servings/week | OR 0.61 (0.006) | Kolonel et al. (2000) |
| Prostate | >3 servings/week | OR 0.50 (0.02) | Cohen et al. (2000) |
| Colon (men) | Top 20% | RR 0.76 (0.011) | Voorips et al. (2000) |
| Colon (women) | Top 20% | RR 0.51 (0.004) | Voorips et al. (2000) |
| Breast | Top 25% | OR 0.05 (0.01) | Fowke et al. (2003) |
| Kidney | Top 25% | OR 0.53 (0.001) | Yuan et al. (1998) |
Source: E.H. Jeffery, Phytochemical Review, 2008.
Sulforaphane works as a potent catalyst to boost Phase 2 enzymes in the body. These detoxification enzymes trigger ongoing antioxidant action for at least 72 hours. As a result, the indirect antioxidant activity of sulforaphane lasts significantly longer than that of direct antioxidants, such as vitamins C, E and beta carotene, although it also boosts the regeneration of the active forms of these vitamins. Furthermore, three-day-old sprouts have a much higher concentration of glucoraphanin than the average mature broccoli (73 mg v. 11 mg per serving, respectively), which means one ounce of broccoli sprouts contains as much glucoraphanin as over 1.25 pounds (20 ounces) of average market-stage broccoli. However, the range of glucoraphanin varies considerably with the variety of broccoli grown, so that in market broccoli, there is at least a 15-fold range of glucoraphanin (Brown et al., J.Am. Hort. Soc. 2002). The highest concentration of glucoraphanin is found in the seed. Eating the raw, unsprouted seed could provide high amounts of sulforaphane, but seeds also contain the antimetabolite erucic acid, which is metabolized during sprouting, so eating seeds is not recommended.
Prepared extracts of either broccoli seeds or broccoli sprouts typically lose their myrosinase activity. As a result, the content of glucoraphanin may remain, but without the presence of the myrosinase, the ability to convert the bioactive sulforaphane has been lost. Based on some limited evidence from animal studies, the colonic microflora may have some myrosinase-like activity. One study suggests this may provide no more than 8% conversion. A human study showed there is such large interindividual variability in the population of colonic microflora in humans, such that any conversion to sulforaphane is not only limited, but also unpredictable. Other researchers have similarly found there is limited sulforaphane bioavailability in broccoli sprouts preparations in which the myrosinase has been destroyed.
The body of scientific knowledge concerning sulforaphane and broccoli sprouts continues to grow at a rapid rate; key studies with respect to broccoli sprouts are summarized below. Although research suggests a promising role for broccoli sprouts in promoting health, the research results do not permit definitive scientific conclusions on specific health benefits. At this time, the US FDA has not reached any such conclusions or authorized any claims specifically for glucoraphanin, sulforaphane or broccoli sprouts.
Summaries of some key studies:
Read more about this topic: Broccoli Sprouts
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