Sniffing out illness, and more.

Health and medicine explained.
Feb. 26 2008 12:47 PM

Your Health This Week

Sniffing out illness—literally. And more.

This week, Dr. Sydney Spiesel discusses a new tool for diagnosing illness by scent, prairie voles who cheat on their mates, and the potential link between nighttime light and breast cancer.

Diagnosis by electro-nose

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Problem: The folklore of medicine is full of stories of master practitioners who would walk into a room, sniff, and make a diagnosis. Hippocrates, for example, is said to have diagnosed diabetes from the characteristic sweet odor of ketones on the breath. Most doctors these days would also be able to diagnose out-of-control diabetes, as well as liver or kidney failure, based on breath scent. Dogs can be trained to recognize bladder cancer by sniffing the urine of patients, and there are claims that honeybees can be trained similarly to detect tuberculosis. But subtler olfactory clues would probably escape us and our animal helpers. To take advantage of this neglected method of diagnosis, we need to either train doctors' noses using the same tools that are used to train wine tasters  or turn to a mechanical nose.

History: Doctors and biomedical engineers have been working on building such a nose since the 1970s. Considerable progress has been made, but until now the required machinery has been too complex, too huge, too expensive, and too narrowly focused to be clinically practical (though one electronic nose was pretty accurate in its ability to diagnose lung cancer from traces of volatile materials in exhaled air).

New method: Enter a recent report about a new and still experimental machine, developed in the laboratories of NIST, formerly the National Bureau of Standards, which marks a turning point in breath analysis. This machine makes use of new laser technology that, in effect, sweeps a huge range of wavelengths of light from ultraviolet to deep infrared through a cavity containing the patient's exhaled air. Computer analysis of the pattern of light frequencies absorbed by materials in the exhaled air can, in principle, be used to detect diseases like asthma, cancer, and liver and kidney failure. The machine is small—about the size of a microwave—and should be simpler, sturdier, and much cheaper than its predecessors. It should also be much more flexible, with the ability to identify a vastly expanded range of breath ingredients.

Caveat: The caveat—a serious one—is that this machine has not yet been tested on real patients with real diseases, though it has been used to detect the same breath ingredients in well people as would identify illness.

Conclusion: Additional development will surely be required before the new electronic nose will be ready for clinical work, but this machine is the first system that looks as if it can be put to practical use. If it lives up to its promise, it will probably turn out to be an extraordinarily powerful new tool for diagnosing serious illness.

Prairie vole
The faithful prairie vole

Sex and prairie voles

Creature: The prairie vole has been a special favorite of traditionalists. Unlike the other 97 percent of mammals, these darling little micelike creatures (with faces that aren't as pointy) favor monogamy. Male and female voles pair off for life. Each makes a nest with a single partner and shares in the care of offspring. When one dies, the surviving partner almost always remains a widow or widower for the rest of its life.

Context: A lot of research has been devoted to finding a neurochemical explanation for the prairie vole's unusual behavior. This work has identified the important roles played by two hormones, oxytocin in females and arginine vasopressin in males. Because human orgasm and breast stimulation are associated with oxytocin release and because humans, like prairie voles, are regarded as a pair-bonding species, it has been almost irresistible to think that prairie voles might provide a neurobiological window onto human love. (Some social conservatives have gone so far as to argue that when humans have sex outside marriage, they damage their oxytocin signaling.)

New research: Alas, new research shows that voles don't quite fit the idealized model for human romantic relationships in the way we've thought. Alexander Ophir and colleagues attached teensy radio collars to a collection of young, sexually inexperienced females and let them loose in a fenced-off natural setting. After a couple of days (to give the females time to scout out nesting sites), the researchers released an equal number of young male voles also fitted with radio collars. The locations of all the animals were tracked electronically. As expected, the males wandered around a bit and then most joined and bonded with females, who became pregnant. After about two and a half weeks, the animals were trapped and euthanized. The embryos were collected from the pregnant females and tested for paternity, using DNA methods.

Findings: The results showed that the voles' social monogamy doesn't always translate into sexual monogamy. One-quarter of the vole females were carrying the baby of a male other than their partner (who, by the way, might well have briefly wandered away from his soul mate for a quick dalliance with a different female).

Conclusion: This will be a disappointment to the prairie voles' traditionalist fans. But as the authors point out, their findings "ironically … suggest that prairie voles are even better models of human attachment than has been appreciated."

Nighttime light and cancer

Potential cause: The factors that contribute to the development of cancer range from dyes to insecticides to X-rays to genetics and also from hormones to viruses to cosmic rays to cigarette smoke. Perhaps the strangest of all is exposure to light at night in relation to breast cancer. At least four strong epidemiological studies have shown that women shift workers, especially those assigned to the graveyard shift, are at roughly one and a half times increased risk for developing breast cancer. The studies (the earliest goes back to 1996) included Danish, Norwegian, Finnish, and American women who worked as caterers, radio operators, and nurses. Because of this observation, shift work is now itself classified as a probable carcinogen.

Question: Why should this be? Is the increased risk simply related to nighttime exposure to light? Or are shift workers perhaps more prone to get cancer because they don't sleep well or enough, or because they experience more stress?

Background: Animal studies have offered a clue: For instance, when mice implanted with human breast cancer tissue are exposed to constant light throughout the night, the average daily growth of the cancer tissue is seven times greater compared with similar animals exposed to light during the day and darkness at night—a strong argument that nighttime light exposure is the critical factor.

New research: Now Itai Kloog and colleagues have studied the link between nighttime light and breast cancer by overlaying satellite maps of Israel showing nighttime light density with similar maps showing clusters of high and low incidence of breast cancer. They found a high degree of coincidence between exposure to light at night and risk of breast cancer. The women living in well-lit and less-lit places differed on a number of other fronts, including ethnicity, birthrate, population density, and income level, so the authors used statistical methods to filter out the influence of those factors on the local cancer rate. With these factors accounted for, the local level of nighttime light was still highly associated with the breast cancer rate.

Rationale: Why would this be? There are many possible explanations, but a good deal of evidence focuses on the role of one hormone, melatonin, which suppresses the growth of some tumors. Melatonin is produced by the pineal gland, which is located deep in the brain and controlled when the eyes detect light or darkness: Darkness stimulates melatonin production, and light exposure suppresses it. Blind people tend to have high blood levels of melatonin, day and night. And blind women have much lower rates of breast cancer than women with sight. We're not sure that the difference is due to the higher levels of melatonin, but that is one hypothesis accepted by many cancer specialists.

Conclusion: Kloog's observation shouldn't be taken as proof of a causal relationship. But it does make you wonder if an increased risk of one kind of cancer is a cost of living and working in an industrial city with work and light around the clock.

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