Hops: benefits, dosage, contraindications

Sedative

The sedative activity of hop extracts has been confirmed in vivo and in humans by an open study of 225 volunteers. In mice, hop extracts showed a dose-dependent reduction in locomotor activity and an increase in the duration of sleep induced by narcotics. The sedative effect has been attributed to the bitter alpha acids and, to a lesser extent, the bitter beta acids and hop oil.

Usages associés

Estrogenic activity

It is thought that the hop strobile flavonoids 8-PN and isoxanthohumol are responsible for the plant's estrogenic activity. The flavonoid 8-PN has the ability to bind to estrogens. Thus, it binds competitively to alpha and beta estrogen receptors, but with a greater affinity for the estrogen receptor beta. Thus, hop extract competitively inhibits the binding of estradiol to estrogen receptors and induces transcription in estrogen-sensitive cells.

Usages associés

Anticancer

Xanthohumol may have potential anticancer activity. Preliminary research suggests that xanthohumol inhibits the metabolic activation of food-borne carcinogens and induces phase II enzymes involved in the metabolism or detoxification of potentially harmful xenobiotics. Xanthohumol and xanthohumol D have also been identified as ligands of quinone reductase-2, which is a target for chemopreventive drugs. In addition to its chemopreventive effects, there is interest in hops and its constituent xanthohumol for prostate cancer. In vitro research suggests that xanthohumol and a derivative can induce apoptosis in benign prostatic hyperplasia and malignant prostate cancer cells. These constituents appear to activate the pro-apoptotic proteins Bax and p53. They also appear to decrease activation of NF-kappaB. Similarly, xanthohumol appears to inhibit the proliferation of liver cancer cells by inhibiting NF-kappaB activity. Some preliminary evidence suggests that hops may possess antiproliferative properties, indicating potential chemoprevention against breast cancer, ovarian cancer, and colorectal cancer. A proposed mechanism includes inhibition of P450 enzymes that activate carcinogens. Further laboratory research shows that the hops constituent 6-prenylnaringenin induces the 2-hydroxylation pathway of estrogens. This pathway has been associated with a reduced risk of breast cancer, possibly through a detoxification effect.

Anti-inflammatory

Preliminary animal research suggests that xanthohumol in hops has anti-inflammatory activity. It appears to inhibit lipopolysaccharide (LPS)-induced production of monocyte chemoattractant protein-1 (MCP-1), TNF-alpha, and interleukin-1 (IL-1) in a human monocytic cell line and in mouse macrophages. Xanthohumol also appears to inhibit LPS-induced production of nitric oxide (NO) and the cytokines IL-1beta and tumor necrosis factor (TNF)-alpha in mouse-derived brain (microglial) cells. Humulone, another constituent of hops, has also shown anti-inflammatory activity in animal research. Humulone may inhibit ear inflammation caused by arachidonic acid in mice. The bitter acids of hops, including alpha acids, beta acids, and iso-alpha acids, have also shown anti-inflammatory activity. Other in vitro research suggests that the rho-iso-alpha acids of hops may inhibit LPS-induced nitric oxide production in macrophage cells, as well as reduce collagen-induced arthritis in an animal model. In humans, hop extract decreases the complement C3 fraction, C-reactive protein levels, and IL-6 levels.

Antioxidant

Preliminary research suggests that xanthohumol in hops has antioxidant effects. Hop chalcones bearing an alpha,beta-unsaturated ketone function have been shown to inhibit oxidation of low-density lipoproteins (LDL). In addition, hop cone extract has been shown to reduce oxidative stress in blood platelets, similarly to resveratrol.

Antimicrobial

Hop essential oils and hop extracts have shown antimicrobial activity against Gram-positive bacteria, Gram-negative bacteria, five strains of acne-causing bacteria, and one species of fungus in vitro. Some research attributes the antibacterial effects of hop to its weak acid derivatives, notably trans-isohumulone, humulone, colupulone, and trans-humulinic acid. Tetrahydroiso-alpha acids have also shown antibacterial effects against Gram-positive and Gram-negative bacteria in vitro. Some research has investigated the antiviral potential of xanthohumol, a component of hop. In vitro research shows that xanthohumol can enhance the antiviral effect of interferon alpha-2b against bovine viral diarrhea virus, a surrogate for hepatitis C virus, suggesting its potential benefit when used with anti-hepatitis C regimens.