health effects

New study suggests that eating nuts prolongs your life – or does it?

A new study published in the New England Journal of Medicine examined consumption of nuts in relation to total mortality.  According to a press release in the Arizona Daily Star “Eating nuts is tied to lower risk of death” “The risk of dying of heart disease dropped 29 percent and the risk of dying of cancer fell 11 percent among those who had nuts seven or more times a week compared with people who never ate them.”

Many studies suggest that eating nuts have a beneficial effect on health.  The study in question was a statistical study of 170,000 health-care professionals that were followed for many years.

The results of the study are consistent with the conclusion that eating nuts every day prolongs life.  However, the results were also consistent with the conclusion that healthier people tend to eat more nuts than less healthy people, so the association is a coincidence.  Correlation does not prove causation.  Hence the study can’t really determine cause and effect.

You can read the complete article in the New England Journal of Medicine here and form your own conclusion.

Here are some details of the study:

“Dietary intake was measured with the use of validated food-frequency questionnaires administered every 2 to 4 years.”  This assumes the respondents correctly remembered, and honestly reported nut consumption.

The study excluded people with history of cancer, heart disease, or stroke.  It also excluded smokers, the extremely thin, the extremely fat, and diabetics.  Therefore, the study selected people who were genetically healthy or who had good health habits.

The study concludes: “In conclusion, our analysis of samples from these two prospective cohort studies showed significant inverse associations of nut consumption with total and cause-specific mortality. Nonetheless, epidemiologic observations establish associations, not causality, and not all findings from observational studies have been confirmed in controlled, randomized clinical trials.”

Although the study did not really prove that nuts prolong life, nuts do have many benefits, so go nuts.

See also:

Statistical Games #1

Statistical Games #2 Stroke for Stroke

Statistical Significance in Science – how to game the system

Some Effects of Volcanic Ash Eruptions

Yesterday I wrote about the geologic setting of the Iceland volcanic eruptions. Fellow blogger Carolyn Classen asked about “vog” the volcanic smog caused by Hawaiian volcanic eruptions.

There is a variety of opinion on the health effects of the volcanic ash. Close to the eruption site, there is a danger from volcanic gases (such as carbon dioxide, fluorine, and sulfur dioxide) to both humans and livestock. In some Hawaiian eruptions the sulfur dioxide produces smog and acid rain. Acid rain can cause crop damage. And from living in Douglas, AZ, when the copper smelter was active, I know that sulfur dioxide really cleans out your sinuses. But for ash dispersed farther away, Britain’s Health Protection Agency said the concentration of ash particles that may reach the ground “is likely to be low and should not cause serious harm.”

According to the U.S. Geological Survey vog (volcanic smog) is a mixture that includes gases but is predominately aerosols (tiny particles and droplets) formed when volcanic gas reacts with moisture, oxygen, and sunlight. It is this unique mixture of gas and aerosols that makes vog both difficult to study and potentially more harmful than either gases or particles alone. What we have learned from limited studies about the aerosols that comprise vog is that most of the aerosols are acidic and are of a size that is readily retained by the lung. Also, studies done in urban areas having similar pollutants show that these types of aerosols degrade lung function and can compromise our immune system. These effects are especially pronounced for children, individuals who have chronic asthma or other respiratory impairments, or those with circulatory problems. Remember, though, that these are studies of mainland urban areas that have similar pollutants, not studies of vog itself.

According to the International Volcanic Health Hazard Network, in most eruptions, volcanic ash causes very few health problems. In fact, officials there say, there is “almost no risk to people” from this particular ash eruption.

Any effects people do feel are likely to be minor. People may experience itchy or irritated eyes, a runny nose, sore throat or dry cough, or they may notice the smell of sulphur or see a dusty haze, the British Health Protection Agency said. Eyes can become painful, itchy, or bloodshot or produce a sticky discharge, and gritty pieces can scratch the cornea, causing abrasions or a non-contagious form of pinkeye. Skin irritation is less common, but if the ash is acidic, skin could redden and become irritated

But those with pre-existing respiratory problems could experience bronchitis or asthma-type symptoms like wheezing and shortness of breath because fine ash particles can irritate airways, causing them to compress, or they can cause the lining to make more secretions inducing coughing and heavy breathing. Livestock and pets may also be affected.

A study of the Soufrière Hills stratovolcano on the Caribbean island of Montserrat which has been erupting since 1995 says that long-term exposure to high levels of volcanic ash could lead to silicosis. (See: http://tinyurl.com/y262a28 )

The ash may be good for the oceans. According to several studies (noted by Scripps Institution of Oceanography) the initial dissolution of volcanic ash in seawater provides an external nutrient source for primary production in ocean surface waters that may stimulate biological drawdown of CO2. Volcanic ash releases large amounts of phosphate, iron, and other “macronutrients and ‘bioactive’ trace metals. These same nutrients produce fertile soils on land.

The ash poses danger to aircraft engines and some instruments such as pitot tubes (for gauging air speed). The danger could last for months. “The problem with the ash is that it’s difficult to detect except in large concentrations, but we don’t know how low a concentration is ‘safe,’ so flight traffic controllers have to err on the side of caution,” said Jonathan Fink, an ASU professor and volcanologist whose specialty is studying volcanoes and their aftermath. “The major danger occurs when ash gets sucked into the engines, melts into glass and then that glass fuses to the engine parts. The ash also damages windows and windscreens, making it hard for pilots to see. Ash has not caused any commercial airliner to crash yet, but it’s come very close.”

The haze of suspended ash will produce beautiful sunsets.