February 19, 2007
Watercress Reduces Oxidative Stress Markers
Watercress reduces oxidative stress when a few ounces are eaten every day for 8 weeks.
The dietary trial involved 30 healthy men and 30 healthy women (including 30 smokers) eating an 85g bag (a cereal bowl full) of fresh watercress every day for eight weeks. The beneficial changes were greatest among the smokers. This may reflect the greater toxic burden or oxidative stress amongst the smokers, as smokers were also found to have significantly lower antioxidant levels at the start of the study compared to the non-smokers.
Here are the major results from eating a daily bowl of watercress:
- significant reduction in DNA damage to lymphocytes (white blood cells), by 22.9 per cent.
- reduction in DNA damage to lymphocytes (white blood cells) when a sample was challenged with the free radical generating chemical hydrogen peroxide, by 9.4%
- reduction in blood triglyceride levels, by an average of 10%
- significant increase in blood levels of lutein and beta-carotene, which have antioxidant activity, by 100% and 33% respectively(higher intakes of lutein have also been associated with a lower incidence of eye diseases such as cataract and age-related macular degeneration).
The reduction in DNA damage argues for a reduced risk of cancer. DNA mutations probably are the biggest cause of cancer.
The abstract for the research paper provides more details:
Results: Watercress supplementation (active compared with control phase) was associated with reductions in basal DNA damage (by 17%; P = 0.03), in basal plus oxidative purine DNA damage (by 23.9%; P = 0.002), and in basal DNA damage in response to ex vivo hydrogen peroxide challenge (by 9.4%; P = 0.07). Beneficial changes seen after watercress intervention were greater and more significant in smokers than in nonsmokers. Plasma lutein and ß-carotene increased significantly by 100% and 33% (P < 0.001), respectively, after watercress supplementation.
What I'd like to know: If this experiment was repeated for a wide range of vegetables how would they rank in potency? How do cabbage, celery, tomatoes, broccoli, radishes, kale, and other vegetables compare?
In this crossover type experiment, the subjects alternately ate or abstained from eating almost six ounces of raw watercress/day. This substantial amount would (presumably) reduce caloric intake and displace other food in the subjects' normal diets. Possibly, the effects seen are due to caloric restriction, or reduced consumption of meat or high fat food.
A quick scan of the literature indicates that most research studies tentatively conclude that both cruciferous and non-cruciferous vegetable consumption reduces DNA damage and raises anti-oxidant status, but not all find this. See:
"No Effect of 600 Grams Fruit and Vegetables Per Day on Oxidative DNA Damage and Repair in Healthy Nonsmokers"
"A Vegetable/Fruit Concentrate with High Antioxidant Capacity Has No Effect on Biomarkers of Antioxidant Status in Male Smokers" http://jn.nutrition.org/cgi/content/full/131/6/1714
(BTW, I found also an interesting study which demonstrates reduced DNA damage in drinkers -
"Inverse correlation between alcohol consumption and lymphocyte levels of 8-hydroxydeoxyguanosine in humans"
http://carcin.oxfordjournals.org/cgi/content/full/22/6/885 - Is this possibly a hormetic effect?)
I wonder how much "publication bias" which favors papers demonstrating positive effects and corporate sponsorship of some studies influences what we see.
Still, it seems that the demographic evidence that fish/vegetarian and Mediteranean-style diets promote health are compelling.
As I recall, a cup of watercress has 7-10 calories. My old recipe for
weight loss was the Watercress Diet, consisting only of 100-150 cups of
watercress per day. I see that I am vindicated.
I notice you often do additional research and provide lots of good links to additional sources of information.
Thank you! I appreciate your efforts and I am sure lots of other people do too.
Every time I see something having to do with antioxidants, I think about an article I read recently that took the position that antioxidants just flat don't work. The sum and substance of the article was that antioxidants always look good in the test tube, but once introduced to the human body, they lose their power. I hope eating watercress does work, though I, for one, would have a hard time eating a cereal bowl full of the stuff every morning. I also wonder if the test group was large enough to produce results that we can count on.
Vitamin antioxidants have been a big disappointment. But we know that foods differ in their health effects. Researchers have shifted a lot of attention toward non-vitamin antioxidants and other non-vitamin compounds in food.
The biggest problem with antioxidants is that intracellularly most free radicals slam into something before they could hit an antioxidant molecule. But outside of cells the odds are better for stopping radicals before they do harm.
Also, free radicals can be attacked by reducing their generation in the first place. Food can reduce or increase oxidative stress. Eat charbroiled meat cooked with charcoal and lighter fluid and you are eating a big dose of reactive species. But choose more wisely and you will not get as many free radicals in your gut and from there into your blood stream.