Thursday, February 11, 2010

LOW-CARB DIET EFFECTIVE AT LOWERING BLOOD PRESSURE

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In a head-to-head comparison, two popular weight loss methods proved equally effective at helping participants lose significant amounts of weight.

But, in a surprising twist, a low-carbohydrate diet proved better at lowering blood pressure than the weight-loss drug orlistat, according to researchers at Veterans Affairs Medical Center and Duke University Medical Center.

The findings send an important message to hypertensive people trying to lose weight, says William S. Yancy, Jr., MD, lead author of the study in the Jan. 25 Archives of Internal Medicine, and an associate professor of medicine at Duke. "If people have high blood pressure and a weight problem, a low-carbohydrate diet might be a better option than a weight loss medication."

Yancy added, “It’s important to know you can try a diet instead of medication and get the same weight loss results with fewer costs and potentially fewer side effects.”

Studies had already indicated that a low-carbohydrate diet and prescription-strength orlistat combined with a low-fat diet are effective weight loss therapies.

But the two common strategies had not been compared to each other, an important omission now that orlistat is available over-the-counter. In addition, few studies provide data on these treatments for overweight patients with chronic health issues.

That’s what made these findings particularly interesting, says Yancy, a staff physician at the Durham VA where the research was conducted. The 146 overweight participants in the year-long study had a range of health problems typically associated with obesity -- diabetes, high blood pressure, high cholesterol, and arthritis.

"Most participants in weight loss studies are healthy and don’t have these problems," he said. "In fact they are often excluded if they do."

The average weight loss for both groups was nearly 10 percent of their body weight. "Not many studies are able to achieve that," says Yancy, who attributes the significant weight loss to the group counseling that was offered for 48 weeks.

In fact, he says "people tolerated orlistat better than I expected. Orlistat use is often limited by gastro-intestinal side effects, but these can be avoided, or at least lessened, by following a low-fat diet closely. We counseled people on orlistat in our study fairly extensively about the low-fat diet."

In addition to achieving equal success at weight loss, the methods proved equally effective at improving cholesterol and glucose levels.

But Yancy said it was the difference in blood pressure results that was most surprising.

Nearly half (47 percent) of patients in the low-carbohydrate group had their blood pressure medication decreased or discontinued while only 21 percent of the orlistat plus low-fat diet group experienced a reduction in medication use.

Systolic blood pressure dropped considerably in the low-carbohydrate group when compared to the orlistat plus low-fat diet group.

"I expected the weight loss to be considerable with both therapies, but we were surprised to see blood pressure improve so much more with the low-carbohydrate diet than with orlistat," says Yancy, who says the mechanism is unclear.

"While weight loss typically induces improvements in blood pressure, it may be that the low-carbohydrate diet has an additional effect." That physiologic effect may be the subject of future studies.

The bottom line, says Yancy, is that many diet options are proving effective at weight loss. But it’s counseling patients on how to best follow the options that appears to be making the biggest impact.

"It is clear now that several diet options can work, so people can be given a choice of different ways to lose weight. But more importantly, we need to find new ways to help people maintain their new lifestyle."

Duke University

VIDEO OF VIRUS IN ACTION SHOWS VIRUSES CAN SPREAD FASTER THAN THOUGHT POSSIBLE

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New video footage of a virus infecting cells is challenging what researchers have long believed about how viruses spread, suggesting that scientists may be able to create new drugs to tackle some viruses.

Previously, viruses were thought to spread by entering a cell, replicating there, and then being released to infect new cells, so that the rate of spread of a virus would be limited by how quickly it could replicate in each cell.

However, a virus called vaccinia spreads in a different and much faster way, according to a new study in the journal Science by researchers from Imperial College London, funded by the Medical Research Council.

Vaccinia is a poxvirus and is the vaccine that was used to eradicate smallpox. Using live video microscopy, the scientists discovered that it was spreading four times more quickly than thought possible, based on the rate at which it replicates.

Videos of virus-infected cells revealed that the virus spreads by surfing from cell to cell, using a mechanism that allows it to bounce past cells that are already infected and reach uninfected cells as quickly as possible.

Early after vaccinia infects a cell, it expresses two viral proteins on the cell surface, which marks the cell as infected. When further virus particles reach the infected cell, these proteins cause the host cell to push out snake-like projections called "actin tails," which drive the virus particles away towards other cells that they can infect. The particles thus bounce from one cell surface to another until they land on an uninfected cell.

In the study, the researchers prevented the virus from making the proteins needed to make the actin tails in the early stages of infecting a cell and showed that this slowed the spread of the virus dramatically.

The researchers believe that other viruses also employ rapid spreading mechanisms. For instance, herpes simplex virus (HSV-1), which causes cold sores, spreads at a faster rate than should be possible given its replication rate. Thus, this phenomenon discovered with vaccinia may be a common feature a viruses.

The discovery may ultimately enable scientists to create new antiviral drugs that target this spreading mechanism.

Lead study author Professor Geoffrey L. Smith, a Wellcome Trust Principal Research Fellow from the Section of Virology at Imperial College London, said: “The ability of viruses to spread rapidly is often critical for their ability to cause disease. Therefore, understanding how viruses spread is fundamental to designing strategies to block spread and thereby prevent disease.”

“For more than 50 years viruses were thought to spread by an iterative process of infection, replication, release and re-infection, so the rate of spread was limited by the speed of replication. However, my colleagues Virginie Doceul, Mike Hollinshead and Lonnerke van der Linden discovered a novel spreading mechanism that is not limited by virus replication rate and accelerates spread dramatically.

“Shortly after infection vaccinia expresses two virus proteins on the cell surface that mark the cell as infected. This effectively says to additional virus particles trying to infect the cell ’I’m infected already, there is no point coming here, you need to go elsewhere.’ And remarkably the virus particles are physically repelled until they find an uninfected cell. Thus the virus can spread quickly to distant uninfected cells without needing to replicate in each cell on the way.”

“This fundamentally changes how we think about virus dissemination and similar strategies may very well be exploited by many viruses,” added Professor Smith.

(Photo: UCL)

Imperial College London

BLOOD PLATELETS CAN REPRODUCE

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University of Utah researchers led an international team of scientists that is the first to report on the previously undescribed ability of platelets to reproduce themselves in the circulation. Their revolutionary findings were published online ahead of print, Jan. 19, 2010, in the journal Blood.

Platelets develop from precursor cells found in the bone marrow, a process that is called thrombopoiesis. During the final stages of thrombopoiesis, platelets are shed from the cytoplasm of their precursors and then enter the bloodstream. Because they lack nuclei, circulating platelets are often referred to as "cytoplasts."

Because DNA resides in the nucleus, platelets were previously considered incapable of reproducing themselves. However, according to this new study led by Hansjörg Schwertz, M.D., and Andrew S. Weyrich, Ph.D., both of the U of U School of Medicine, platelets are actually capable of giving rise to new platelets.

"Cells with nuclei typically split into two uniform daughter cells that share identical genetic information," says Schwertz, research assistant professor of surgery and lead author of the study. "In our experiments, we found that platelets increase in number by generating beaded extensions that resemble a pearl necklace. Development of these extensions, which contain two or more new platelets, does not require a nucleus."

Schwertz and his colleagues found that the newly formed platelets are structurally and functionally indistinguishable from normal platelets and are similar in size, shape, and metabolic activity. Importantly, the group also demonstrated that platelets produce progeny in human whole blood cultures. This suggests that new treatments may be devised to increase circulating platelet numbers in patients whose platelet counts are abnormally low because of a medical condition.

Platelets are one of the most abundant cells in the bloodstream and their primary function is to halt bleeding. Decreased platelet counts can increase a person's risk for bleeding complications. Conversely, if platelet counts are too high or platelets inappropriately stick to one another, individuals may be at increased risk for vascular disorders such as heart attacks.

In additional studies conducted in cooperation with Robert C. Blaylock, M.D., medical director of transfusion services at the University of Utah and professor of pathology, the group found that platelets used for transfusion are also capable of generating new platelets, even after they are stored in bags for five days. This suggests that platelet numbers may be expanded after they are removed from the body, a finding that could have a significant impact on transfusion medicine.

"More research is needed to understand how platelets reproduce themselves and whether newly formed platelets are identical to, or distinct from, the platelets that are formed directly from their bone marrow precursors," says Weyrich, professor of internal and molecular medicine at the University of Utah's Eccles Institute of Human Genetics and corresponding author of the study. "Nevertheless, our findings identify a new function of platelets that has important bench-to-bedside implications."

University of Utah

LAST NEANDERTHALS DIED OUT 37,000 YEARS AGO

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The last Neanderthals in Europe died out at least 37,000 years ago – and both climate change and interaction with modern humans could be involved in their demise, according to new research from the University of Bristol published in PLoS ONE.

The paper, by Professor João Zilhão and colleagues, builds on his earlier research which proposed that, south of the Cantabro-Pyrenean mountain chain, Neanderthals survived for several millennia after being replaced or assimilated by anatomically modern humans everywhere else in Europe.

Although the reality of this ‘Ebro Frontier’ pattern has gained wide acceptance since it was first proposed by Professor Zilhão some twenty years ago, two important aspects of the model have remained the object of unresolved controversy: the exact duration of the frontier; and the causes underlying the eventual disappearance of those refugial Neanderthal populations (ecology and climate, or competition with modern human immigrants).

Professor Zilhão and colleagues now report new dating evidence for the Late Aurignacian of Portugal, an archaeological culture unquestionably associated with modern humans, that firmly constrains the age of the last Neanderthals of southern and western Iberia to no younger than some 37,000 years ago.

This new evidence therefore puts at five millennia the duration of the Iberian Neanderthal refugium, and counters speculations that Neanderthal populations could have remained in the Gibraltar area until 28,000 years ago.

These findings have important implications for the understanding of the archaic features found in the anatomy of a 30,000 year old child unearthed at Lagar Velho, Portugal. With the last of the Iberian Neanderthals dating to many millennia before the child was born, ‘freak’ crossbreeding between immediate ancestors drawn from distinct ‘modern’ and ‘Neanderthal’ gene pools cannot be a viable explanation. The skeleton’s archaic features must therefore represent evolutionarily significant admixture at the time of contact, as suggested by the team who excavated and studied the fossil.

Professor Zilhão said: “I believe the ‘Ebro frontier’ pattern was generated by both climatic and demographic factors, as it coincides with a period of globally milder climate during which oak and pine woodlands expanded significantly along the west façade of Iberia.

“Population decrease and a break-up of interaction networks probably occurred as a result of the expansion of such tree-covered landscapes, favouring the creation and persistence of population refugia.

“Then, as environments opened up again for large herbivore herds and their hunters as a result of the return to colder conditions, interaction and movement across the previous boundary must have ensued, and the last of the Neanderthals underwent the same processes of assimilation or replacement that underpin their demise elsewhere in Europe five millennia earlier.”

The dating was undertaken by experts at the University of Vienna (VERA laboratory) led by Professor Eva Maria Wild, and at the University of Oxford's Radiocarbon Accelerator Unit.

Professor Wild, head of the 14C program at VERA (Vienna Environmental Research Accelerator) said: “Accurate 14C dating was crucial for this study. For layer 2 of the cave sediment we achieved this by selecting teeth for 14C dating and by comparing the 14C results of the same sample after different, elaborate sample pre-treatments. Agreement between the results obtained with different methods provides a proof for accurate dating.”

(Photo: PLoS ONE)

University of Bristol

SWEET FUTURE: FLUCTUATING BLOOD GLUCOSE LEVELS MAY AFFECT DECISION MAKING

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Would you choose to receive a small amount of money today or a larger sum next month? We know that it is worth it to wait longer for a larger reward, but sometimes the temptation for the smaller, immediate reward becomes too great and we simply cannot resist it. Selecting the immediate reward is known as "future discounting" and often suggests a lack of self-control.

Studies have indicated that there may be a link between blood glucose levels (our body's energy) and thinking. For example, making difficult choices uses up cognitive resources (or brain power) and these resources can be restored by increasing blood glucose.

Psychological scientists X.T. Wang and Robert D. Dvorak from the University of South Dakota investigated how blood glucose levels impact the way we think about present and future rewards. Volunteers answered a series of questions asking if they would prefer to receive a certain amount of money tomorrow or a larger amount of money at a later date. They responded to seven of these questions before and after drinking either a regular soda (containing sugar) or a diet soda (containing the artificial sweetener aspartame). Blood glucose levels were measured at the start of the experiment and after the volunteers drank the soda.

The results, reported in Psychological Science, a journal of the Association for Psychological Science, reveal that people's preferences for current versus later rewards may be influenced by blood glucose levels. The volunteers who drank the regular sodas (and therefore had higher blood glucose levels) were more likely to select receiving more money at a later date while the volunteers who drank the diet sodas (and who had lower blood glucose levels) were likelier to opt for receiving smaller sums of money immediately. These findings are suggestive of an adaptive mechanism linking decision making to metabolic cues, such as blood sugar levels.

The results indicate that when we have more energy available (that is, higher levels of blood glucose), we tend to be more future-oriented. The authors note that "the future is more abstract than the present and thus may require more energy to process. Blood glucose as brain fuel would strengthen effortful cognitive processing for future events." Conversely, having low energy (or low blood glucose levels) may make an individual focus more on the present. The finding that a diet soda drink increased the degree of future discounting suggests that artificial sweeteners may alarm the body of imminent caloric crisis, leading to increased impulsivity.

The authors conclude that if controlling blood glucose levels may affect our decisions for later versus current rewards, then "reducing the degree of fluctuation in blood glucose may offer a possible means for the treatment and intervention of some impulsive disorders, anorexia, drug addiction, and gambling addiction."

Psychological Science

HIS OR HERS JEALOUSY? STUDY OFFERS NEW EXPLANATION FOR SEX DIFFERENCES IN JEALOUSY

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When South Carolina Governor Mark Sanford was caught red-handed returning from a tryst with his Argentine mistress last June, he told the Associated Press that he had met his “soul mate.” His choice of words seemed to suggest that having a deep emotional and spiritual connection with Maria Belen Chapur somehow made his sexual infidelity to his wife Jenny Sanford less tawdry.

What the two-timing governor didn’t understand is that most women view emotional infidelity as worse, not better, than sexual betrayal. This may explain why Hillary Clinton stayed with Bill Clinton and seemed unconcerned about his sexual affair with Monica Lewinsky. Research has documented that most men become much more jealous about sexual infidelity than they do about emotional infidelity. Women are the opposite, and this is true all over the world. The prevailing theory is that the difference has evolutionary origins: Men learned over eons to be hyper-vigilant about sex because they can never be absolutely certain they are the father of a child, while women are much more concerned about having a partner who is committed to raising a family.

New research now suggests an alternative explanation. The new study does not question the fundamental gender difference regarding jealousy—indeed it adds additional support for that difference. But the new science suggests that the difference may be rooted more in individual differences in personality that result from one’s relationship history but that can fall along gender lines.

Pennsylvania State University psychological scientists Kenneth Levy and Kristen Kelly doubted the prevailing evolutionary explanation because there is a conspicuous subset of men who like most women find emotional betrayal more distressing than sexual infidelity. Why would this be? The researchers suspected that it might have to do with trust and emotional attachment. Some people—men and women alike—are more secure in their attachments to others, while others tend to be more dismissive of the need for close attachment relationships. Psychologists see this compulsive self-reliance as a defensive strategy—protection against deep-seated feelings of vulnerability. Levy and Kelly hypothesized that these individuals would tend to be concerned with the sexual aspects of relationships rather than emotional intimacy.

Similar to earlier studies examining sex differences in jealousy, Levy and Kelly asked men and women which they would find more distressing—sexual infidelity or emotional infidelity. Participants also completed additional assessments including a standard and well validated measure of attachment style in romantic relationships.

Findings confirmed the scientists’ hypotheses. As Levy & Kelly report in Psychological Science, a journal of the Association for Psychological Science, those with a dismissing attachment style— who prize their autonomy in relationships over commitment—were much more upset about sexual infidelity than emotional infidelity. And conversely, those securely attached in relationships—including securely attached men—were much more likely to find emotional betrayal more upsetting.

The scientists state that these findings imply that the psychological and cultural-environmental mechanisms underlying sex differences in jealousy may have greater roles than previously recognized and suggest that jealousy is more multiply determined than previously hypothesized.

Additionally, placing jealousy within an attachment theoretical perspective, highlights the value of a taking a more nuanced approach relative to earlier research, points to new research possibilities, and suggests that promoting secure attachment may be an effective means of reducing the kind of sexual jealousy that contributes to domestic violence.

Psychological Science

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