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Broccoli, Green Tea, Inhibits Flu Virus Infection in Human Nasal Cells
Researchers at North Carolina University's, Center for Environmental Medicine, in Chapel Hill, have identified how two nutritional supplements, EGCG, an extract from green tea, and sulforaphane, a compound from raw broccoli, increase the expression of Nrf2, accounting for a significant decrease in influenza virus entry, and replication, in human nasal cells. An additional effect was identified. In the absence of infection, the activety of Nrf2 via nutritional supplements SFN and EGCG increased baseline response of antiviral agents, RIG-I, IFN-beta, and MxA, suggesting a protective effect against flu infections. Researchers of this study comment how the nutritional influence of phase II antioxidant enzyme pathways of EGCG and sulforazone may prove to be an attractive therapy for virus inflamation and immune clearance. Their research was published in the Free Radical Biological Medicine, April 2011.(1)
Broccoli is a rich source of glucoraphanin, the glucosinolate precursor of sulforaphane. Evidence suggests how sulforaphane can reduce and prevent influenza infection, inflammation and cancer. Other cruciferous vegetables considered for their immune building effects are Brussels sprouts, garden cress, mustard greens, turnip, cabbage (savoy), kale, watercress, kohlrabi, cabbage (red), broccoli, horseradish, cauliflower and bok choi.
Bioavailable Vegetables - Raw or Cooked?
Thorough chopping, or chewing, of raw broccoli helps to improve metabolism and bioavailability by releasing the catalyst myrosine, which provides an increased breakdown of glucosinolates, that translates into biologically active compounds called isothiocyanates.(2)
The myrosinase catalyst in cabbage is completely destroyed by heat, however the myrosinase activity of human intestinal bacteria allows for some formation and absorption of isothiocyanates. (3).
The absorption and excretion of isothiocyanates is significantly higher from raw vegetables than from cooked. (2, 4, 5) Glucosinolates are water soluble, migrating from plant cells into hot water when boiled. Boiling vegetables for 9 to 15 minutes results in a 18 to 59% decrease in glucosinolates.(52) Using less water, such as steaming or microwaving, may reduce the loss of glucosinolate. However, some cooking practices, including boiling (2), steaming (4, 58), and microwaving at high power (750-900 watts) (5, 58, 59), inactivate myrosinase, the enzyme that catalyzes glucosinolate.
Several studies have found that consuming five, or more servings per week of cruciferous vegetables provides a significant reduction in cancer risk. (6-8)
Glucosinolate Content | ||
| Food (raw) | Serving | Total Glucosinolates (mg) |
| Brussels sprouts | ½ cup (44g) | 104 |
| Garden cress | ½ cup (25g) | 98 |
| Mustard greens | ½ cup, chopped (28g) | 79 |
| Turnip | ½ cup, cubes (65g) | 60 |
| Cabbage, savoy | ½ cup, chopped (45g) | 35 |
| Kale | 1 cup, chopped (67g) | 67 |
| Watercress | 1 cup, chopped (34g) | 32 |
| Kohlrabi | ½ cup, chopped (67g) | 31 |
| Cabbage, red | ½ cup, chopped (45g) | 29 |
| Broccoli | ½ cup, chopped (44g) | 27 |
| Horseradish | 1 tablespoon (15g) | 24 |
| Cauliflower | ½ cup, chopped (50g) | 22 |
| Bok choi (pak choi) | ½ cup, chopped (35g) | 19 |
Food Sources of Isothiocyanates | ||
| Isothiocyanate | Glucosinolate (precursor) | Food Sources |
| Allyl Isothiocyanate (AITC) | Sinigrin | Broccoli, Brussels sprouts, cabbage, horseradish, mustard, radish |
| Benzyl Isothiocyanate (BITC) | Glucotropaeolin | Cabbage, garden cress, Indian cress |
| Phenethyl-Isothiocyanate (PEITC) | Gluconasturtiin | Watercress |
| Sulforaphane (SFN) | Glucoraphanin | Broccoli, Brussels sprouts, cabbage |
References
1. Kesic MJ, Simmons SO, Bauer R, Jaspers I. Nrf2 expression modifies influenza A entry and replication in nasal epithelial cells. PMID: 21549835
2. Shapiro TA, Fahey JW, Wade KL, Stephenson KK, Talalay P. Chemoprotective glucosinolates and isothiocyanates of broccoli sprouts: metabolism and excretion in humans. Cancer Epidemiol Biomarkers Prev. 2001;10(5):501-508. PMID: 11352861
3. Shapiro TA, Fahey JW, Wade KL, Stephenson KK, Talalay P. Human metabolism and excretion of cancer chemoprotective glucosinolates and isothiocyanates of cruciferous vegetables. Cancer Epidemiol Biomarkers Prev. 1998;7(12):1091-1100. PMID: 9865427
4. Conaway CC, Getahun SM, Liebes LL, et al. Disposition of glucosinolates and sulforaphane in humans after ingestion of steamed and fresh broccoli. Nutr Cancer. 2000;38(2):168-178. PMID: 11525594
5. Rouzaud G, Young SA, Duncan AJ. Hydrolysis of glucosinolates to isothiocyanates after ingestion of raw or microwaved cabbage by human volunteers. Cancer Epidemiol Biomarkers Prev. 2004;13(1):125-131. PMID: 14744743
6. Feskanich D, Ziegler RG, Michaud DS, et al. Prospective study of fruit and vegetable consumption and risk of lung cancer among men and women. J Natl Cancer Inst. 2000;92(22):1812-1823. PMID: 11078758
7. Giovannucci E, Rimm EB, Liu Y, Stampfer MJ, Willett WC. A prospective study of cruciferous vegetables and prostate cancer. Cancer Epidemiol Biomarkers Prev. 2003;12(12):1403-1409. PMID: 14693729
8. Michaud DS, Spiegelman D, Clinton SK, Rimm EB, Willett WC, Giovannucci EL. Fruit and vegetable intake and incidence of bladder cancer in a male prospective cohort. J Natl Cancer Inst. 1999;91(7):605-613. PMID: 14693729