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Tuesday, May 31, 2011

Drinking Too Much Water Can Be Harmful And Even Fatal

Drinking large quantities of water has been widely promoted over the past few years as a means of maintaining health, improving appearance, controlling weight, and preventing dehydration. It is now not unusual to see people regularly carrying and sipping from water bottles. Eight 8-ounce glasses of water a day has been commonly recommended as the minimum requirement. However, the evidence shows that this recommendation has little scientific basis. In addition, excess water consumption can be harmful and even fatal.

A June 4, 2009 article by Karen Bellenir, in the online Scientific American, a highly-respected journal, analyzed the origins of the 8 glass a day recommendation and presented the opinions of scientists in the area of hydration. The conclusion was that there was no scientific basis for the recommendation. Some key points from the article:
  • Most people do not have to drink 64 ounces of water per day.
  • Water needs differ widely among individuals and depends on many factors including body size, physical activity, ambient temperature and humidity.
  • Much of our fluid needs are met from the water content in food.
  • The only people who benefit from drinking large amounts of water are those who sweat a lot due to their participation in heavy physical activity, especially in hot environments, and people with specific medical conditions such as kidney stones or urinary tract infections.
  • For hydration purposes, all drinks composed largely of water, including milk, juice, coffee, and tea are roughly equivalent to drinking plain water. While caffeine does somewhat stimulate urination, the net effect of these drinks is to provide the body with water. Only alcoholic beverages cause a net water loss.
  • Drinking when thirsty is the best means of meeting our physiological need for fluid.
  • Drinking water before meals does not reduce appetite or food consumption. However, eating foods that contain a lot of water but few calories (e.g. salad vegetables, fruit) can help control appetite.
One might think that excessive water-drinking is relatively harmless, with the only downsides being a bloated stomach, frequent urination, the expense of buying water and the inconvenience of carrying it. However, excessive water-drinking can actually be harmful and even fatal, as revealed in a June 21, 2007 article by Coco Ballentyne in the Scientific American online. Fatalities cited in the article include those of a woman who died after drinking 6 liters of water in a radio-station sponsored contest to see who could hold their urine the longest and an aspirant to a college fraternity who was prompted to drink excessive amounts of water. In addition, several athletes and military personnel have died after drinking excessive quantities of water in an effort to avoid dehydration.

The cause of these deaths is hyponatremia, which is a dangerously low concentration of sodium in the blood. Warning symptoms of this disorder include frequent urination, fatigue, headache, nausea, vomiting, and disorientation. Much of the damage is caused by entry of the excessive water into brain cells, with resultant brain swelling and damage.

It particularly dangerous for people engaged in endurance sports to drink excessive water because such physical activity stimulates the secretion of a hormone that tends to conserve water in the body by reducing excretion, even when drinking is excessive. This can reduce the kidneys’ ability to remove water from the bloodstream by 90%. Sport drinks, which contain sodium and other electrolytes as well as carbohydrates can help in preventing dangerous dilution of the blood, yet even excessive drinking of these fluids can cause hyponatremia. Drinking to thirst is still seen as the best recommendation.

Another possible negative effect of drinking too much water is the effect on blood pressure. A study by Callegaro et al. published in the Journal of Human Hypertension (vol. 21, pp. 564-570, July 2007) concluded that, after ingesting 500 ml (a little over 2 cups) of water, the systolic blood pressure of both subjects with and without high blood pressure rose 17-19 points and the diastolic blood pressure rose 14 points. These are major increases. While other studies did not observe this effect, it appears that excess water consumption may increase the possibility of high blood pressure. Thus, drinking to thirst is the best means of taking an amount of water that will avoid both dehydration and hyponatremia.

Monday, May 2, 2011

Omega-3 Fats from Fish Oil Raise Risk of High-Grade Prostate Cancer

It has been increasingly evident that there are trade-offs in the quest to get and stay healthy. In other words, there are actions we can take that will reduce the risk of one health problem, but increase the risk of another. One example is playing high-impact sports such as basketball, which is great for improving and maintaining physical fitness while having fun, but also increases the risk of sprains, strains and other musculoskeletal problems. Now, an article by Brasky et al. in the American Journal of epidemiology (published online April 24, 2011)  points up a trade-off involved in taking fish-oil supplements, which have been widely recommended for reducing the risk of cardiovascular diseases and other health problems.

The researchers analyzed blood samples of 3,461 men to measure levels of omega-3 fats (DHA and EPA from fish consumption), omega-6 fats (from common vegetable oils), and trans-fats (from hydrogenated oils in margarine, shortening, and processed foods). The men were then followed over a 7-year period in order to see the association of the different fat types to the incidence of prostate cancer. The hypotheses were that:
  • Because of the anti-inflammatory effect of the omega-3 fats, men with the highest blood levels of them would have a lower incidence of prostate cancer
  • Because of the inflammatory effect of the trans- fats, men with the highest blood levels of them would have a higher incidence of prostate cancer
The statistical analysis produced the following surprising results:

   > There were no effects of any of the fat types on overall incidence of prostate cancer.
   > When looking at the high-grade form of prostate cancer that progresses rapidly and is the most lethal:
  • Those men with the highest blood levels of DHA from fish oil had more than twice the risk of contracting high-grade prostate cancer as men with the lowest blood levels of DHA.
  • EPA from fish oil had no effect on the incidence of high-grade prostate cancer.
  • Those men with the highest blood levels of trans-fats had about half the risk of contracting high-grade prostate cancer as men with the lowest blood levels of trans-fats
  • Blood levels of the type of omega-3 fat from vegetable sources (e.g. flax seeds, walnuts) had no effect on the incidence of high-grade prostate cancer.
Bottom Line
The results of highly surprising, given the widespread view of fish oil as all-good and trans-fats as all-bad. Here is a clear case of trade-off. There is considerable evidence that fish-oil is good for the heart and cardiovascular system and reduces the incidence of heart attacks. Yet, here we see that it increases the risk of high-grade prostate cancer. Eating omega-3 fats from flax-seeds or other vegetable sources is not a solution because that type of omega-3 fat has not been proven to reduce the risk of cardiovascular disease. The good news is that most prostate cancer is of the low-grade variety. Given that heart disease remains the number one killer of both men and women, it doesn’t appear that fish and fish-oil be abandoned as a health-promoting dietary elements. Yet men must be aware of the trade-off in risk of eating fatty fish or taking fish-oil supplements in order to make an informed decision about how best to promote their health.

Update (May 8, 2011):, a company that tests the quality of supplements from various companies, contacted Dr. Theodore Brasky, the lead author of the study described herein. He stated that the blood levels of DHA and EPA measured in the study were largely based on fish consumption rather than fish-oil supplements. However, a recent study of his, soon to be published, shows no link between fish oil supplementation and risk of prostate cancer. He also noted another study (Szymanski, Am J Clin Nutr 2010) that found fish consumption associated with a large reduction in late state or fatal prostate cancer.