I can almost hear my mother saying it, except that it was about vegetables in general, and it was in Yiddish.

A recent study coming out of the University of Ulster (Good news from Northern Ireland???) found that the salad leaf, known in the 19th Century as “poor man’s bread”, can inhibit the growth of cancer cells and even kill them.

An item in the UK News reports,

“In a trial, a group of 30 men and 30 women aged between 19 and 55, including 30 smokers, each ate an 85g bag—a cereal bowl full—of watercress every day for two months as well as their normal diet.

Watercress reduces DNA damage to white blood cells which is considered an important trigger in the development of cancer. It raises antioxidants which mop up free radicals which in turn damage proteins and DNA and can lead to the hardening of arteries.

The biggest improvement in antioxidant levels was found amongst the smokers, who had significantly lower levels at the beginning of the study, which is published in the American Journal of Clinical Nutrition this month.

The results of the study showed a 22.9% reduction of DNA damage to white blood cells. There was also an increase of 100% in blood levels of lutein, which protects against eye diseases such as cataracts and age-related macular degeneration, and an increase of 33% in beta carotene. Intakes of dietary fiber, vitamins C and E, and folate were also significantly higher during the two-year study.

The study, which was funded by the Watercress Alliance, which is made up of British watercress producers, Vitacress Salads, Alresford Salads, and The Watercress Company, was inspired by a previous study demonstrating the anti-cancer properties of watercress on colon cancer cells.

Published in May 2006, the previous study showed for the first time that watercress helped prevent the initiation of DNA damage which triggers cancer development and the growth and spread of cancer cells, which are the three key stages of carcinogenesis, the process that causes cancer.”


Should we believe it?

I tend to give the study the benefit of the doubt. After all, we do know that green leaf vegetables are “good for you”. They contain folic acid, a very important vitamin B, as well as variable amounts of antioxidants. So, what are my reservations?

  • The study was funded by the British Watercress Producers. Studies funded by Industry are notorious for their optimistic conclusions and their ultimate irreproducibility. Here in the U.S., blueberries were in vogue because of their prodigious antioxidant content. That study was funded by the Blueberry Growers Association. I am not aware of any follow-up study confirming any of the claims that had been made. In the pharmaceutical field, it is well documented that studies sponsored by the drug industry are much more optimistic than the actual clinical experience proves to be.

The study design has some significant flaws. For instance, in a good study, there should always be a control group; in this case, a group eating a normal diet without watercress. Furthermore, the numbers are small; to draw any statistical inferences, the groups have to be much larger. I would have also liked to see a group eating another green leaf vegetable to demonstrate the superiority of watercress. All dark green vegetables are an excellent source of folic acid. In fact, folic acid inhibited the powerful effect of caffeine, a well-known agent used in the laboratory to affect DNA fragmentation (don’t quit your morning coffee yet—the concentrations used in such laboratory experiments are unrealistically high).


The conclusion?

My mother was right. Eat lots of vegetables—they are all good for you (it sounds a lot better in Yiddish), and if you eat a mixture of them, you cover all your bases. I am sure that watercress would make a nice addition to any salad, regardless of its alleged therapeutic properties.

Finally, why was watercress called “a poor man’s bread”? In the 19th Century, it was a staple part of the working class diet, with people starting their day off with a watercress sandwich for breakfast. And if they were too poor to buy bread, people would eat a bunchful on its own, giving it the nickname “poor man’s bread”.

Dov Michaeli, MD, PhD
Dov Michaeli, MD, PhD loves to write about the brain and human behavior as well as translate complicated basic science concepts into entertainment for the rest of us. He was a professor at the University of California San Francisco before leaving to enter the world of biotech. He served as the Chief Medical Officer of biotech companies, including Aphton Corporation. He also founded and served as the CEO of Madah Medica, an early stage biotech company developing products to improve post-surgical pain control. He is now retired and enjoys working out, following the stock market, travelling the world, and, of course, writing for TDWI.