Lifetime Medical Costs Of Obese People Actually Lower Than Costs For Healthy And Fit, Mathematical Model Shows

Daily Science Journal (Feb. 8, 2008) — A new research paper suggests that preventing obesity might result in increased public spending on medical care. Many countries are currently developing policies aimed at reducing obesity in the population. However, it is not currently clear whether successfully reducing obesity will also reduce national healthcare spending or not. Pieter van Baal and colleagues, from the National Institute for Public Health and the Environment in the Netherlands, created a mathematical model to try to answer this question.

Researchers found that the group of healthy, never-smoking individuals had the highest lifetime healthcare costs, because they lived the longest and developed diseases associated with aging; healthcare costs were lowest for the smokers, and intermediate for the group of obese never-smokers. (Credit: iStockphoto/Eliza Snow)

In their study, van Baal and his co-workers created three hypothetical populations of 1000 men and women, all aged 20 years at the start: a group of obese, never-smoking individuals; a group of healthy-never smoking individuals of normal weight; and a group of smokers of normal weight. The model produced an estimate of the likely proportion of each group who would encounter certain long term (chronic) diseases, and then estimated what the approximate cost of medical care associated with each disease was likely to be. The researchers found that the group of healthy, never-smoking individuals had the highest lifetime healthcare costs, because they lived the longest and developed diseases associated with aging; healthcare costs were lowest for the smokers, and intermediate for the group of obese never-smokers.

However, the authors argue that although obesity prevention may not be a cure for increasing expenditures, it may well be a cost-effective cure for much morbidity and mortality and importantly contribute to the health of nations.

A Perspective by Klim McPherson, from Oxford University in the UK, who was not involved in the study, discusses the implications of these findings and comments that "it would be wrong to interpret the findings as meaning that public-health prevention (e.g., to prevent obesity) has no benefits"; the quality of life experienced by individuals, and other factors, must also be taken into account when planning interventions aimed at improving public health.

Citation: van Baal PHM, Polder JJ, de Wit GA, Hoogenveen RT, Feenstra TL, et al. (2008) Lifetime medical costs of obesity: Prevention no cure for increasing health expenditure. PLoS Med 5(2): e29. doi:10.1371/journal.pmed.0050029 http://medicine.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pmed.0050029

Adapted from materials provided by Public Library of Science, via EurekAlert!, a service of AAAS.

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Why Serotonin Can Cause Depression And Anxiety

Daily Science Journal (Feb. 5, 2008) — Mood disorders could be caused by a loss of our inherent, reflexive avoidance of aversive events, according to a new study. Researchers from UCL in London and Columbia University in New York used computational modeling techniques to integrate what appeared to be blatant contradictions between serotonin's roles in different states of health.

Serotonin appears to be one of the major players in mood and a variety of other disorders. But exactly how remains an open question. Imagine walking past a dark alleyway in a dangerous part of some city; although it might be a shortcut, most people wouldn't consider taking it. In healthy subjects, serotonin appears important for this automatic avoidance.

It has long been suggested that over-activity of the serotonin system may relate to mood disorders such as depression and anxiety, as these seem characterized by too much withdrawal and avoidance. However, the new modeling study simply suggests that we think about what happens when these reflexes fail--suddenly you have to think hard to avoid things that used to be avoided reflexively You might for example consider walking down the dangerous alley, be robbed and thus be reminded and taught by additional experience that dark alleys are to be avoided.

In this study Prof. Peter Dayan and Dr. Quentin Huys built a reinforcement learning model of reflexive choices. Agents take actions and as a result of these move through a set of states, some of which are rewarded or punished. As agents progress through this space, they learn the value of each state--how much punishment or reward is to be expected from this state onwards.

It turns out that adding to the agent's behavioural repertoire a simple reflex, which guides the agent away from an action with potential for poor consequences, does two things: it increases the rewards reaped overall, but, because bad states are now not explored any more, it also prevents them from learning exactly how bad these bad states are. When serotonin drops, say in depression or anxiety, agents have no more recourse to the reflexive avoidance and have to rely on what they learned. Because they have not learned how bad the bad states are, they start exploring states that don't look too bad to them, but in reality are much worse. Serotonin enhancing drugs, such as Prozac, are then suggested to reinstate the reflexive avoidance, and thus to redress the balance.

This study gives insight into some puzzling findings--for example, it argues that the association of depression with aggression may have to do with a lack of reflexive avoidance of it. In addition, stress not only causes depression, but people with depression experience more stressors. Again, this may be related to a dysfunctional reflexive avoidance system. The study, however, vastly oversimplifies a number of issues, such as the flexibility of reflexive actions, and the effect of non-reflexive action choice. These provide interesting avenues for further research, and may in fact give some insight into the co-morbidity of different mood disorders.

Journal citation: Dayan P, Huys QJM (2008) Serotonin, inhibition, and negative mood. PLoS Comput Biol 4(1): e4. doi:10.1371/journal.pcbi.0040004. http://compbiol.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pcbi.0040004

Adapted from materials provided by PLoS Computational Biology, via EurekAlert!, a service of AAAS.

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Computer Models Suggest Planetary And Extrasolar Planet Atmospheres

Daily Science Journal (Jun. 21, 2007) — The world is abuzz with the discovery of an extrasolar, Earth-like planet around the star Gliese 581 that is relatively close to our Earth at 20 light years away in the constellation Libra.

Artist's impression of the five-Earth mass planet, Gliese 581 c, found in the habitable zone around the red dwarf Gliese 581, with the instrument HARPS on the ESO 3.6-m telescope. (Credit: European Southern Observatory)

Bruce Fegley, Jr., Ph.D., professor of earth and planetary sciences in Arts & Sciences at Washington University in St. Louis, has worked on computer models that can provide hints to what comprises the atmosphere of such planets and better-known celestial bodies in our own solar system.

New computer models, from both Earth-based spectroscopy and space mission data, are providing space scientists compelling evidence for a better understanding of planetary atmospheric chemistry. Recent findings suggest a trend of increasing water content in going from Jupiter (depleted in water), to Saturn (less enriched in water than other volatiles), to Uranus and Neptune, which have large water enrichments.

"The farther out you go in the solar system, the more water you find," said Fegley.

Fegley provided an overview of comparative planetary atmospheric chemistry at the 233rd American Chemical Society National Meeting, held March 25-29, 2007, in Chicago. Fegley and Katharina Lodders-Fegley, Ph.D., research associate professor of earth and planetary sciences, direct the university's Planetary Chemistry Laboratory.

"The theory about the Gas Giant planets (Jupiter, Saturn, Uranus, and Neptune) is that they have primary atmospheres, which means that their atmospheres were captured directly from the solar nebula during accretion of the planets," Fegley said.

Gas Giants

He said that Jupiter has more hydrogen and helium and less carbon, nitrogen and oxygen than the other Gas Giant planets, making its composition closer to that of the hydrogen- and helium-rich sun. The elements hydrogen, carbon and oxygen are predominantly found as water, the gases molecular hydrogen and methane and in the atmospheres of the Gas Giant planets.

"Spectroscopic observations and interior models show that Saturn, Uranus and Neptune are enriched in heavier elements," he said. "Jupiter, based on observations from the Galileo Probe, is depleted in water. People have thought that Galileo might just have gone into a dry area. But Earth-based observations show that the carbon monoxide abundance in Jupiter's atmosphere is consistent with the observed abundances of methane, hydrogen and water vapor. This pretty much validates the Galileo Probe finding."

The abundances of these four gases are related by the reaction CH4+H20 = CO+3H2. Thus, observations of the methane, hydrogen and CO abundances can be used to calculate the water vapor abundance. Likewise, Earth-based observations of methane, hydrogen and carbon monoxide in Saturn's atmosphere show that water is less enriched than methane.

In contrast, observations of methane, hydrogen and carbon monoxide in the atmospheres of Uranus and Neptune show that water is greatly enriched in these two planets. Although generally classed with Jupiter and Saturn, Uranus and Neptune are water planets with relatively thin gaseous envelopes.

"On the other hand, the terrestrial planets Venus, Earth and Mars have secondary atmospheres formed afterwards by outgassing — heating up the solid material that was accreted and then releasing the volatile compounds from it," Fegley said. "That then formed the earliest atmosphere."

He said that by plugging in models he's done on the outgassing of chondritic materials and using photochemical models of the effects of UV sunlight, he and his collaborator Laura Schaefer, a research assistant in the Washington University Department of Earth and Planetary Sciences, can speculate on the atmospheric composition of Earth-like planets in other solar systems.

"With new theoretical models we are able to surmise the outgassing of materials that went into forming the planets, and even make predictions about the atmospheres of extrasolar terrestrial planets," he said.

"Because the composition of the galaxy is relatively uniform, most stars are like the sun — hydrogen-rich with about the same abundances of rocky elements — we can predict what these planetary atmospheres would be like," Fegley said. "I think that the atmospheres of extrasolar Earth-like plants would be more like Mars or Venus than the Earth."

Fegley said that photosynthesis accounts for the oxygen in Earth's atmosphere; without it, the Earth's atmosphere would consist of nitrogen, carbon dioxide and water vapor, with only small amounts of oxygen. Oxygen is 21 percent of Earth's atmosphere; in contrast, Mars has about one-tenth of one percent made by UV sunlight destroying carbon dioxide.

"I see Mars today as a great natural laboratory for photochemistry; Venus is the same for thermochemistry, and Earth for biochemistry," he said. "Mars has such a thin atmosphere compared to Earth or Venus. UV light can penetrate all the way down to the Martian surface before it's absorbed. That same light on Earth is mainly absorbed in the ozone layer in the lower Earth stratosphere. Venus is so dense that light is absorbed by a cloud layer about 45 kilometers or so above the Venusian surface."

Adapted from materials provided by Washington University in St. Louis.

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