BACKGROUND:Hops have long been used to make beer, but they also have a long, though less well known, history of medicinal use. Hops are harvested from a climbing vine that only grows at certain latitudes: not too far south because the plant requires long hours of daylight to blossom, but not too far north as it cannot survive harsh winters. They have been cultivated in northern Europe since the ninth century, and Germany remains the largest producer. The part harvested is called a strobile, which is a cone-like flower structure which contains numerous overlapping scales. Only female strobiles are harvested for either beer or herbal remedies.
Hops are used in beer production to add flavour and to act as a preservative. Such uses have been known for many centuries, with other medicinal uses proposed in only the last century or two. Hops have been used medicinally for many different purposes, most commonly to treat mild anxiety and to promote sleep. Apart from the usual teas and capsules, pillows filled with hops are available with claims that the aroma is sufficient to help people sleep.
EVIDENCE FROM STUDIES
A substance called lupulin (from hops’ scientific name, Humulus lupulus) was isolated from hops in 1813. Anecdotal reports claimed that lupulin promoted sleep, although others claimed it didn’t help at all. In 1983, a substance was purified from lupulin and produced sedation in several animal studies. Laboratory studies have shown that the compound interacts with various natural sleep-causing mechanisms.
Most of the clinical research on hops has used products that contain hops along with other herbs, most commonly valerian. One German product containing valerian (187mg) and hops (42mg) showed changes in people’s brainwave activity consistent with inducing sleep. A randomised controlled trial compared valerian with the valerian plus hops product in people with insomnia. Those taking the combination product took less time to fall asleep than those taking valerian alone. However, the results have not been consistent. In three randomised controlled trials of the combination product, some ways of measuring sleep quality showed improvements but others showed no improvements. There are also conflicting reports on how quickly the product works. One study found no difference in sleep quality after two weeks, but improved sleep after four weeks. Another found that one dose of the combination led to improved sleep.
One of the first randomised controlled trials of hops alone was published in June 2010. In adults with chronic insomnia, sleep quality improved by over 60 per cent in both groups, but with difference between those taking hops and those taking a placebo. This highlights the importance of the placebo effect in studying conditions like insomnia.
PROBLEMATIC ASPECTS
In general, remedies containing hops are safe if taken in small amounts. If hops produce a sedative effect, this could interfere with other sedatives or anti-depressants. Anyone already taking such medications should talk to a doctor or pharmacist before starting hops.
Hops and lupulin contain a small amount of oestrogen-like substances. The amount in beer or herbal remedies is extremely small, but concerns have been raised for people with oestrogen-sensitive cancers, including breast, uterine and cervical cancers. People with these cancers should probably avoid remedies with hops.
RECOMMENDATIONS
Hops have a long history as a remedy for mild anxiety and insomnia. Laboratory research has shown that hops contain sleep-inducing compounds, although the results of clinical trials are not clear-cut. In addition, very little information is available on hops alone, with most research conducted on hops combined with valerian.
Given that these remedies have been shown to be safe for most people, a trial period could be warranted. It is usually recommended to take the remedy an hour before going to bed. If improvements are to occur, they usually appear within a few weeks.
Dónal O'Mathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a senior lecturer in the School of Nursing, Dublin City University
