Low-salt diet prevents heart attacks and strokes

Eating less salt can reduce the risk of cardiovascular disease by 25% and cut the risk of death from all causes by a fifth, according to a new study.

The 15-year study of 2400 people demonstrates for the first time that cutting back on salt can reduce the risk of diseases such as stroke and heart attack, in addition to lowering blood pressure.

Volunteers in the study who were assigned to a low-salt regime had a 20% lower risk of death from all causes over the course of the study than their control counterparts. The findings should compel governments to take more action to reduce the salt content of processed foods, says Nancy Cook at the Brigham and Women's Hospital in Boston, Massachusetts, US, who led the study.

Numerous studies have documented how consuming foods high in salt can lead to high blood pressure. This happens because the salt draws more water into the blood, and the increase in fluid volume exerts more pressure on vessel walls. High blood pressure is known to contribute to heart disease, but few studies have shown a direct link between salty foods and the condition.

Salt snapshot

In the late-1980s and early-1990s Cook and colleagues collected urine samples from more than 3000 people with above-normal blood pressure. Analysing the urine samples collected over the course of a 24-hour-period gave the researchers a snapshot of the subjects' salt intake. On average, they were consuming 10 grams of salt per day.

Cook's team then randomly assigned half of these participants to attend weekly workshops that taught how to cook low-salt meals and read nutrition labels on packaged foods.

After approximately three months of this nutrition counselling, urine sampling revealed that the subjects reduced their daily salt intake by about 3 grams per day on average – the equivalent of about half a teaspoon.

Fifteen years later Cook's team was able to obtain follow-up health information about 2415 of the participants from medical records and telephone interviews.

Healthy choices

Phone interviews indicated that those who had received training on how to reduce their salt intake many years ago continued to consume less of it than their control counterparts. For example, 47% of those who received this intervention said they looked for reduced-salt foods in the supermarket, compared with 29% of the control group.

Of the 200 people who had developed cardiovascular disease – including heart attacks and stroke – in the past 15 years, 112 had received no dietary recommendations and 88 were in the group taught to reduce their salt intake.

After controlling for factors such as weight and age, the researchers calculated that reducing one's salt intake by 30% could decrease the risk of cardiovascular disease by 25%.

Cook says that the results of the study should encourage governments to "work with the food industry to come up with lower sodium foods", and notes that salt content is highest in processed and fast-foods. "People generally consume much more salt than what is biologically needed."

In 2006, the American Medical Association urged the US Food and Drug Administration to revoke the "generally recognised as safe" (GRAS) status of salt and to adopt stricter salt guidelines.

Current US dietary guidelines recommend that people consume less than one teaspoon of salt per day.

Journal reference: BMJ (DOI: 10.1136/bmj.39147.604896.55)

Genes versus heat – a reptile sex trigger

High temperatures can make an Australian lizard that is genetically male develop into a female. The finding throws new light on how sex is determined in reptiles.

For most reptiles, a gene on a sex chromosome triggers an embryo to develop as either a male or a female. In some species, males have an X and a Y chromosome, while females are XX, as in mammals. In other species of lizards, males are ZZ while females are ZW, as in birds.

But for a third group of reptiles, which includes all crocodiles, alligators and marine turtles, temperature, rather than a gene on a sex chromosome, triggers either male or female differentiation. Extreme low or high temperatures generally lead to more females.

Now a team led by Alex Quinn at Canberra University in Australia has found that the central bearded dragon (Pogona vitticeps) is susceptible to both types of sex trigger, and that temperature can override its genetic gender.

Transitional form

When the team incubated eggs at relatively high temperatures – between 34°C and 37°C – the majority of embryos that had ZZ sex chromosomes (genetically male), hatched as females. The team thinks the bearded dragon represents a transitional form, in evolutionary terms, between the two main methods of sexual determination.

The research shows that, for the bearded dragon at least, the W chromosome is not necessary in producing a female. The team suspects that a double dose of a particular gene on the Z chromosome is instead crucial for maleness, and that this gene is inactivated by high temperatures.

“The possibility that there is a male-determining, dosage-dependent gene on the Z chromosome of bearded dragons is an important insight,” says Quinn, “because to date, scientists have discovered the master sex-determining gene only in mammals and a single species of fish.”

The team plans to hunt for that master gene in the bearded dragon. They also want to investigate how widespread the phenomenon of temperature sex reversal really is in reptiles.

If many other reptiles with sex chromosomes are also susceptible to temperature, this would broaden the number of species that could be vulnerable to climate change.

“The concern is that the current rate of climate warming could be too rapid for these species to adapt to, and this could potentially result in heavily skewed sex ratios, and even population crashes in some cases,” Quinn says.

Journal reference: Science (vol 316, p 411)

Regular aspirin use may protect cancer

Regular aspirin use may protect more than just your heart - it could also reduce your risk of getting cancer.

Aditya Bardia and colleagues at the Mayo Clinic College of Medicine in Rochester, Minnesota, analysed the cancer history of more than 22,000 post-menopausal women over 12 years. Those who reported taking aspirin regularly at the start of the study were 16 per cent less likely to develop cancer and 13 per cent less likely to die from it during that time. The only lifestyle factor that influenced the results was smoking, which reduced the protective effect slightly.

Bardia says aspirin's anti-inflammatory action is probably responsible, although a similar effect
was not seen with other anti-inflammatories, such as ibuprofen. The findings were presented at a meeting of the American Association for Cancer Research in Los Angeles this week.

From issue 2600 of New Scientist magazine, 23 April 2007, page 16

Cambridge Scientists Produce Live Video Showing How Carbon Nanotubes Form

A Cambridge University-led team of scientists have successfully produced live video footage that shows how carbon nanotubes, more than 10,000 times smaller in diameter than a human hair, form.

The video sequences show nanofibres and nanotubes nucleating around miniscule particles of nickel and are already offering greater insight into how these microscopic structures self-assemble. The films can be viewed on the Cambridge University website at:


http://www.admin.cam.ac.uk/news/special/20070301/

In particular, the team discovered that the carbon network is guided into tubular shape by a drastic restructuring of the nickel – the catalyst in the process. They were also able to track and time the deposition of the carbon around the nickel.

Carbon nanotubes are new building blocks enabling engineers to improve and further miniaturise everyday electronic devices like computers or mobile phones. At the moment scientists can grow nanotubes but cannot accurately control their structure.

Being able to do so is vital as it is the very structure of a nanotube that dictates its properties. The nano-scale video observations mean that scientists will be able to better understand the nucleation of nanotubes and are therefore an important step on the route towards application.

The two sequences show action taking place in real time on an astonishingly small scale. The difference in size between a single-walled nanotube and a human hair is close to the difference between the same human hair and the Eiffel Tower. The microscopic scale involved has, in the past, made it difficult to understand the growth process.

The team used X-rays produced at a synchrotron (a type of particle accelerator) and a modified high-resolution transmission electron microscope to observe and film a process called catalytic chemical vapour deposition. This is one of several methods of producing nanotubes, and involves the application of a gas containing carbon (in this case acetylene) to minute crystalline droplets referred to as “catalyst islands” (the nickel).

As the gas is applied carbon sticks to the catalyst islands forming layers of graphite. In conditions appropriate to creating nanofibres, the nickel particle was pushed upwards in a series of peristaltic movements as the carbon continued to deposit on its sides. At several points the nickel formed a cap which almost “popped” out of the forming tube, leaving a layer of graphite behind it. This process is called “bambooing”, because the resultant carbon nanofibre is a cylinder containing several cavities, each one separated by one of these graphite layers, similar in form to bamboo. Throughout the whole process, the nickel remained crystalline rather than liquid.

The team then looked at conditions more appropriate to producing single-walled carbon nanotubes, which involved less acetylene. The catalyst is not squeezed upwards. Instead, a cap of carbon formed on the top of the nickel, and gradually extended from it to form a tubular structure. The catalyst island was squeezed and reshaped by this process and was moulded by the carbon forming around it rather than retaining its original form.

Dr Stephan Hofmann, who led the research, said: “In order to reach the full application potential for nanotubes, we need to be able to accurately control their growth first. As a manifestation of the impressive progress of nanometrology, we are actually now able to watch molecular objects grow. This new video footage shows that the catalyst itself remains crystalline but is constantly changing its shape as the carbon network is formed around it.

“We cannot yet solve the problem of not being able to self-assemble carbon nanotubes with well-defined characteristics, but we have discovered that if we are to do so, we need to be mindful not just of the carbon dynamics but the changing shape of the catalyst as well.”

source :- http://www.cam.ac.uk