Friday, September 28, 2012

A Water Desalination Plant for San Diego

Only 1% of Earth’s water is fresh water; 97% is saltwater and the remaining 2% is frozen in glaciers. Worse yet, water is not evenly distributed around the world. Growing cities frequently have problems getting enough fresh water to supply their needs.

The city of San Diego, after years of dealing with water shortages and expensive water sources, has decided to take matters into its own hands. The city signed a deal this week to purchase all of the output of what will be the largest desalination plant in the Western hemisphere, if/when it is completed in 2016. The new plant, to be located in Carlsbad, California, is expected to produce 50 million gallons of freshwater a day

Desalination of seawater may seem like a good idea, but it has yet to catch on in a big way. For one, desalination uses a lot of electricity, and thus is still fairly expensive compared to most natural sources of water. In addition, by removing the salt from seawater and returning it to the sea, desalination plants can raise the local seawater salinity, affecting sea life if the salt is not sufficiently disbursed.

The Carlsbad desalination plant is likely to be watched with interest by officials from other coastal cities with water shortages. Either it will prove to be a one-of-a-kind project that didn’t go quite as well as planned, or it will lead the way to the development of other desalination plants for supplying water to other thirsty coastal cities.

Wednesday, September 26, 2012

BPA and Childhood Obesity

Last week a scientific article in the Journal of the American Medical Association indicated that there is an association between childhood obesity and bisphenol A (BPA), a plastic used to coat the inside of food cans. The authors of the report measured the concentrations of BPA in urine (a rough measure of BPA exposure) in over 2,800 children. They found that the most obese quartile of the children also had the highest levels of urinary BPA. The authors were quick to point out (correctly) that the observed association between obesity and high concentrations of BPA does not prove that BPA causes obesity. Although the findings are certainly intriguing, there are other possible explanations. For example, perhaps the obese children were obese because they ate more food (ingested more calories) from containers lined with BPA, so that their high BPA levels are just a consequence of where they got their calories. Or perhaps obese children store more BPA in their fat. Incidentally, the authors based their findings on data obtained from questionnaires, a notoriously poor way to obtain accurate information about dietary intake.

In science, words matter.  The headlines of most popular press news coverage of the JAMA article correctly used phrases like “an association” or “a link” to describe the relationship between obesity and BPA. Others were not so careful; the headline in the International Business Times was “BPA Causes Obesity in Children, New Study Shows”.

Unfortunately, such sloppy (or agenda-driven) reporting of science news only scares and confuses consumers. The American Chemistry Society, admittedly a group that itself might have an agenda, felt obligated to issue a press release on BPA this week, pointing out that the study’s authors themselves stated “…causation cannot be inferred from a cross-sectional association…”.

I’m not trying to defend BPA; frankly I think the jury is still out concerning its risk to human health. In the face of uncertainty, though, there’s nothing wrong with deciding to err on the side of caution and cutting down on the use of BPA in food containers, especially if suitable substitutes can be found. For example, BPA has already been removed from babies’ bottles. But the American Chemisty Society is right; the evidence presented in the most recent study does not prove that BPA causes or even contributes to childhood obesity. This time, the International Business Times just plain got it wrong.

Tuesday, September 18, 2012

Ultrasound Enhances Transdermal Drug Delivery

Most medical drugs are administered as an injection or are taken orally as pills or liquids.  Both drug delivery methods have their drawbacks; injection requires at least some technical expertise and the availability of sterile syringes and needles and also involves some pain.   Oral ingestion is not very effective for proteins and other macromolecules that are easily degraded by the digestive system.

The idea that ultrasound could be used to enhance the delivery of drugs directly across the skin (transdermal delivery) has been around for many years.  Progress was slow until about two decades ago, when it was discovered that low-frequency sound waves (20-100 kHz) were more effective than the higher frequencies (700 kHz and above) being used at the time.  If you’re interested, see the review on this subject published in 2010.

A potential breakthrough in the field came this month when the same authors who wrote the 2010 review published new data showing that using both low- and high-frequency ultrasound together caused better drug absorption across the skin than using either frequency alone.   A proposed mechanism for the enhancement is described in the paper, reviewed this week by ScienceDaily.

A lot of work still needs to be done (including safety and effectiveness studies and finally FDA approval) before ultrasound-enhanced drug delivery becomes commonplace.  But its likely that in your lifetime, you’ll be prescribed a therapeutic drug in a cream or ointment form and given a small hand-held ultrasound device to enhance its absorption through the skin.

Sunday, September 9, 2012

First Drug Approved for HIV Prevention

For the first time, the U.S. Food and Drug Administration (FDA) has approved a drug specifically for the prevention of sexually-acquired HIV infection. The drug, called Truvada, is currently being used in combination with other drugs in the treatment of existing HIV infections.

Not everyone is happy about the FDA’s decision. The main concern is that using the drug in a large number of uninfected individuals could increase the risk of the HIV virus becoming resistant to the drug. To reduce that possibility, the FDA is asking health professionals to prescribe the drug only to high at-risk individuals (such as partners of HIV-infected persons) who have been tested for HIV and are currently negative. In addition, individuals who are taking the drug should be retested every three months to ensure that they remain negative, because Truvada alone is not recommended for HIV-infected individuals. But retesting for HIV status every three months is asking a lot in terms of compliance by health professionals and patients.

Health officials will be watching closely for any signs of the development of resistance of the HIV virus to Truvada. Whether or not patients on Truvada actually comply with the HIV re-testing recommendation will be of interest, too.

Thursday, September 6, 2012

Organic Foods Are Not More Nutritious

If you’ve watched a newscast this week you can hardly have missed it.  News flash!  Organic foods are no more nutritious than conventional foods.  There seemed to be a self-righteous tone to some of these reports, as if the “discovery” proved something important (or gave the reporter a justification for NOT choosing organic foods him/herself :).

In the study highlighted in the news this week, researchers at Stanford University reviewed and summarized virtually all the data available from 223 previous studies in which the nutritional value of organic and conventional foods were compared.  Taken together, the studies showed no significant difference in nutritional value between organic and conventional foods.  And in the very few studies in which the health effects of eating organic foods were assessed, there were no obvious health benefits, either.  In essence, this is not "new" news, but a rehash of old news.

And so what?  People who choose organic foods don’t necessarily choose them because they think they are more nutritious.  The primary concern of most organic food buyers is a belief that the ingestion of pesticides and herbicides is harmful, especially to pregnant women and young children.  And yes, the researchers DID find that organic foods had fewer (and lower) pesticide residues than conventional foods.   (Most news reports were quick to point out that the levels of pesticides in conventional foods were within acceptable limits according to current regulations).  By the way, where organic foods get their pesticide residues is not clear; contamination of equipment used to harvest or transport organic foods, blow-by of spray from nearby non-organic farms, even cheating by organic farmers are all possibilities.

Some people choose organic foods out of concern for the environmental impact of excessive use of pesticides and other chemicals, such as antibiotics.   Others think they may taste better; still others wish to support smaller local organic farmers.  These are certainly valid reasons. So choose organic foods if you wish and if you can afford them – just don’t do it because you believe they are more nutritious.

Monday, September 3, 2012

Caloric Restriction and Longevity, Revisited

Does severe caloric restriction really lead to longer life? Back in 2009, a research study from the University of Wisconsin (performed with primates) suggested that it does. But now a second study, also in primates, seems to contradict that finding. The latest study, from the respected National Institute on Aging, began 25 years ago and is still ongoing. But the data so far show no positive effect of caloric restriction on longevity. These findings are corroborated by experiments in 41 different strains of mice that showed that caloric restriction has little or no effect on life span overall – it increased length of life in some strains, had no effect in others, and actually reduced lifespan in some strains.

Why the contradictions? No one is sure, but certainly there were differences in how the two primate studies were done. The initial study omitted some primates from inclusion in the final statistics, arguing that they did not die from “age-related” causes. There were differences in diets used as well.

It’s still possible that caloric restriction does lead to some health benefits other than simply length of life. Indeed, in the most recent primate study, caloric restriction did seem to lower cholesterol and sugar levels in some of the monkeys. But the current data are not particularly encouraging when it comes to the efficacy of caloric restriction in extending life span.

For more on this subject, go to a previous blog post titled "Caloric Restriction and Longevity."