Thursday, August 27, 2009

Can You Taste Bitter Foods?

About 25% of the human population does not perceive vegetables such as broccoli, cabbage, or Brussels sprouts as bitter-tasting. The rest of us perceive these vegetables as either mildly bitter or obviously bitter. These differences are determined by a gene that has two variations, or alleles – one for “bitter taster” and one for “non-taster”. The bitter taster allele is dominant, so if you have at least one copy of it you will perceive Brussels sprouts as mildly or intensely bitter.

At what point in human evolution did the ability to taste bitter foods first appear? Recent DNA analysis of a bone of a Neanderthal (an extinct line of archaic humans) indicates that they possessed the bitter taster allele. Therefore, the ability to taste bitter foods probably evolved more than half a million years ago, before Neanderthals and modern humans diverged from a common ancestor.

Evolutionary biologists believe that the ability to perceive bitter taste may have discouraged early humans from eating bitter-tasting plants, some of which are toxic if ingested in large quantities.

Thursday, August 20, 2009

Measuring Groundwater Depletion

Scientists are using satellite data to measure changes in the amount of water in underground aquifers. How do they do it? Satellite speed is affected by the pull of gravity, which is partly determined by how much water is underground near Earth's surface. As the first of two satellites approaches a region of the Earth with a large underground aquifer, the pull of gravity increases and the satellite speeds up briefly, increasing the distance between it and a trailing satellite. As the second satellite passes over it too speeds up briefly, closing the gap again. By measuring the changes in distance between the two satellites as they pass over the aquifer and then comparing those distances from year to year, scientists can determine changes in the pull of gravity over time and then estimate how much water has been gained or lost.

Using this technology, scientists have discovered that in just six years, one of the largest aquifers in India has lost a volume of water equal to a lake 30 feet deep and nearly 5,000 square miles in surface area. Most of the groundwater consumed in the region is used for agriculture. Nobody knows how large the aquifer really is or how long it would take to deplete it, but losses of this size just are not sustainable in the long run.

We can expect more of this kind of useful information as the satellite technique becomes more sophisticated. But will we choose to change our water use practices as a result of what we learn?

Saturday, August 15, 2009

Breast-Feeding and Breast Cancer

A recent study in the Archives of Internal Medicine raises the possibility (but does not entirely prove) that breast-feeding may lower the risk of breast cancer among women at high risk for the disease. The study gathered data from over 60,000 women who had reported at least one pregnancy by 1997. Among women with close relatives who developed breast cancer, those who breast-fed for a period of time had only 41% as many breast cancers by 2005 as women who had never breast-fed. The lowered cancer incidence was only seen among women at high risk for breast cancer; women with no family history of breast cancer did not benefit from breast-feeding.

Why doesn’t this study prove once and for all that “breast-feeding prevents cancer”? Because it only shows an association between breast-feeding and lowered cancer risk - cause-and-effect has not been proved. Perhaps women who choose to breast-feed are more health-conscious overall. Perhaps they exercise more or have a better diet, and that’s actually what lowered the cancer risk. Further research will be needed to tease out the details.

Wednesday, August 12, 2009

Is Running Hard on Knees?

Runners are often told (usually by non-runners) that running is hard on their knees. According to commonly held belief, the constant pounding wears out or damages knee cartilage and leads to either knee injury or an increased likelihood of osteoarthritis later in life.

But the available scientific evidence suggests that running is not a risk factor for knee osteoarthritis, and may in fact keep you healthier later in life. In one study, runners were compared to age-matched non-runners over an 18-year period. There was no difference in the rate of development of osteoarthritis between the two groups. In another study, overall disability rates in runners increased at only one quarter of the rate seen in age-matched sedentary persons.

A major risk factor for knee osteoarthritis is not running per se; its having had a previous knee injury. That is why there is so much osteoarthritis among former N.F.L. football players and former soccer players. But if you’re a recreational runner and manage to stay injury-free, don’t worry about wearing out your knees – just keep running!

Thursday, August 6, 2009

The Spleen Stores Monocytes

Shortly after severe tissue damage such as that caused by a heart attack or an infection, the number of monocytes, the white blood cells that eventually mature into macrophages, increases dramatically in the blood. These new monocytes appear too quickly to have been newly produced from stem cells in bone marrow. So where do they come from?

Apparently they come from the spleen. The spleen stores up to ten times as many monocytes as there are in the bloodstream at any one time. When a tissue is injured the spleen releases its stored monocytes, which then migrate to the site of injury, develop into macrophages, and participate in the cleanup and repair process. It’s a pretty efficient use of resources, when you think about it - a virtual army of monocytes is kept on standby, ready to be deployed when needed.

Monday, August 3, 2009

Buying/Selling Kidneys

A Brooklyn businessman named Levy-Izhak Rosenbaum was arrested in New Jersey in 2009 for allegedly trying to broker the purchase of a kidney for $160,000. According to the criminal complaint filed against him, Mr. Rosenbaum told an undercover agent that he could arrange for a live kidney donor from Israel, and that they would then fabricate a fictitious “relationship” between the donor and the recipient so that the hospital in the U.S. would not become suspicious.

The Rosenbaum case is just one example of the shadowy black market in human organs worldwide. The World Health Organization estimates that about 10% of the more than 60,000 kidneys transplanted each year come from living donors who have sold their kidneys strictly for money. The temptation is hard to resist, especially for donors from poor countries where the choice may come down to selling a kidney or selling a child. The practice is not even illegal in some countries (Pakistan is an example), and as a result those countries are rapidly developing thriving “transplant tourism” enterprises.

What, if anything, could be done about the shortage of organs for transplantation?

Saturday, August 1, 2009

What Happened to the Neandertals?

The cover story of the August 2009 issue of Scientific American discusses the latest evidence and hypotheses for why the archaic humans called the Neandertals disappeared from Europe around 28,000 years ago. Older theories, that the Neandertals either interbred with modern humans or died in wars against them (the love versus war hypotheses), seem to be losing favor. A more recent hypothesis is that there were frequent and rapid changes in climate in Europe at the time, and that modern humans, by virtue of being more advanced in certain ways, were better able to adapt to the changes in weather and food supplies. The article goes on to describe the likely cultural, behavioral, and biological differences between the Neandertals and modern humans who lived in Europe 35,000 years ago, and how these differences might have affected modern humans’ success or the Neandertals’ ultimate failure.