Daily Archives: 11 October 2012

Death by chocolate

Chocolate may have some health benefits, but too much of a good thing can kill you. But it’ll kill your dog more quickly.

One of the key components of chocolate is theobromine, or theobromide, also known as xantheose. It has the chemical formula C7H8N4O2 and it is a bitter alkaloid of the cacao plant – although it’s also found in tea leaves and the kola (or cola) nut. Despite its name, the compound does not contain the element bromine (Br). The name comes from Theobroma, meaning “food of the gods”, the genus of the cacao tree.

It also comes from caffeine: when caffeine is metabolised in the liver, 12% of it is turned into theobromine.

Theobromine is a vasodilator (i.e., it widens blood vessels), a diuretic (makes you urinate) and a heart stimulant. As a result, it can be poisonous.

Fortunately, the median lethal dose for humans is 1000 milligrams per kilogram of body weight. That means that an 80 kg human would have to eat 5.7 kg of unsweetened dark chocolate for it to kill them (going by a theobromine content of 14 milligrams per gram of dark chocolate, although it varies). For milk chocolate, you’d have to eat around 40 kg.

However, domestic animals metabolise it much more slowly than humans. Dogs are the most vulnerable, with a median lethal dose of only 300 milligrams per kilogram of body weight. Although cats do have a lower toxic dose – 200 mg/kg – they’re unable to taste sweetness and so are much less likely to eat enough chocolate.

The first signs of theobromine poisoning are nausea, vomiting, diarrhea, and increased urination. In high doses it goes on to cardiac arrhythmias, epileptic seizures, internal bleeding, heart attacks and eventually death. The half-life of theobromine in dogs is 17.5 hours, and if they’ve eaten enough of it the symptoms can persist for 72 hours.

A typical 20 kg dog will normally experience intestinal distress after eating less than 240 g of dark chocolate, but won’t necessarily experience brachycardia or tachyarrhythmia unless it eats at least 500 g of milk chocolate.

Remember though that humans aren’t totally immune, and the elderly are particularly vulnerable to consumption of large quantities. There have been extreme cases when people have had to go to the emergency room.

But it is your dog you have to watch, so try not to give them chocolate. Or if you can’t stop them, you can find a nifty online theobromine toxicity calculator at AskAVetQuestion.com

I’m looking through you

This month marks the 50th anniversary of The Beatles’ first single, Love me do, and the beginning of their contribution to medical science.

It goes like this: in 1967, Godfrey N. Hounsfield, an engineer working for Electric and Musical Industries Ltd, came up with a way to see soft tissues of the body with X-rays. On a conventional X-ray, bones are much easier to see, with organs like lungs and the brain being only indistinct blurs. But you can get some idea of them by comparing X-rays taken from different sides, like viewing the lungs from the chest and the back.

Hounsfield’s idea was to scan using X-rays from all angles around a person, and then put them together with the aid of computers. This technique came to be called computed tomography, or a CT scan. You’ve probably seen them before: a patient lies on a bed and then an enormous X-ray machine rotates around them. Each scan takes a 2-dimensional slice, and by putting them together it’s possible to build a full, 3-dimensional, even real-time, view of the body’s inner workings.

The first scan by a commercial CT machine was performed on 1 October 1971 in Atkinson Morley Hospital in Wimbledon, England. Eight years later, Hounsfield was awarded the Nobel Prize in Physiology or Medicine for his achievements, sharing it with Allan M. Cormack (Cormack was an American physicist who initially developed a theory of computer-assisted tomography, but his method wasn’t used in the commercial systems).

What does this have to do with The Beatles? Well, Hounsfield’s employer is abbreviated as EMI, which of course was The Beatles’ record label. It was thanks to the gold mine of their musical success – about 200 million singles – that EMI was able to fund Hounsfield’s research over four years to develop his device from a prototype into something that could be used as a hospital.

The Beatles’ music has inspired many people, but their scientific contribution has saved more lives.

The Beatles greatest gift… is to science (The Whittington Hospital NHS Trust)
Goodman LR 2010, “The Beatles, the Nobel Prize, and CT scanning of the chest”, Radiologic Clinics of North America, vol. 48, no. 1, pp. 1-7, PMID: 19995626

Sick cities

Older Australians living in urban areas are more likely to have a long-term health problem than those in rural or remote locations, with people from disadvantaged areas faring the worst of all.

Recent research from the University of Sydney looked at the correlation between environmental factors and non-infectious chronic disease in the ageing population using 1,256 survey participants, aged over 45, who had lived in the same location for at least 20 years (Black D, O’Loughlin K, Kendig H & Wilson L 2012, “Cities, environmental stressors, ageing and chronic disease”, Australasian Journal on Ageing, no. 31, pp. 147–151, doi: 10.1111/j.1741-6612.2011.00552.x).

The non-infectious diseases they considered included conditions like type 2 diabetes, arthritis, cancer and asthma, all of which are suspected to be affected by environmental risk factors, or stressors.

A woman with a case and a thin man sitting on a park bench in Jackson Square, New Orleans in 1935 (click to embiggen)
Parks and other green spaces in urban areas are believed to be good for the health of our ageing population (photo by Ben Shahn, via Wikimedia Commons)
As lead author Professor Deborah Black said:

“In the city you’re exposed to a range of environmental stressors, such as poor air quality, aircraft and road noise, high density housing, lack of adequate transport, poor urban design, a lack of green spaces and shade trees, and so on.”

“As people get older, their bodies are less able to cope physiologically with environmental stressors, and exposure can accelerate the ageing process and trigger or exacerbate disease.”

Low socioeconomic status was a big factor in this, with those living in the most disadvantaged areas having a 90 per cent greater chance of having a long-term health condition. These areas, with the cheapest housing, are often also near industrial areas, airports or busy roads, and also have reduced access to health services and public transport.

Urban health problems are expected to only worsen with climate change, as the heat island effect causes paved areas to reach higher temperatures, to which the elderly are more susceptible. This suggests that it’s important to try and improve urban environments by maintaining green spaces among the bitumen and concrete.