Friday, December 07, 2007

Importance of a Good Night's Sleep (Update)

Back in March I linked to this study which suggested that a good night's sleep is important for forming new memories. Well, two further studies published this month show the stakes are even higher. The first report is "Carcinogenicity of shift-work, painting, and fire-fighting" in the latest issue of Lancet Oncology. Anyone who has worked shifts (which I did for a couple of summers when I worked in a steel factory) will know that if can wreak havoc on one's life (from sleep and eating habits to social life). This report from researchers at the International Agency for Research on Cancer suggests that shift work can also increase risk of cancer. Here is a sample:

About 15–20% of the working population in Europe and the USA is engaged in shift-work that involves nightwork, which is most prevalent (above 30%) in the health-care, industrial manufacturing, mining, transport, communication, leisure, and hospitality sectors. Among the many different patterns of shiftwork, those including nightwork are the most disruptive for the circadian clock.

Six of eight epidemiological studies from various geographical regions, most notably two independent cohort studies of nurses engaged in shiftwork at night, have noted a modestly increased risk of breast cancer in long-term employees compared with those who are not engaged in shiftwork at night. These studies are limited by potential confounding and inconsistent definitions of shiftwork, with several focused on a single profession. The incidence of breast cancer was also modestly increased in most cohorts of female flight attendants, who also experience circadian disruption by frequently crossing time zones. Limitations of studies in these flight attendants include the potential for detection bias, proxy measures of exposure, and potential uncontrolled confounding by reproductive factors and cosmic radiation.

Several different rodent models have been used to test the effect of disruption of the circadian system on tumour development. More than 20 studies investigated the effect of constant light, dim light at night, simulated chronic jet lag, or circadian timing of carcinogens, and most showed a major increase in tumour incidence. No clear effect was seen for light pulses at night or constant darkness. A similar number of studies investigated the effect of reduced nocturnal melatonin concentrations or removal of the pineal gland (where melatonin is produced) in tumour development and most showed increases in the incidence or growth of tumours.

And the latest issue of American Journal of Epidemiology has an interesting study entitled "Do Childhood Sleeping Problems Predict Obesity in Young Adulthood? Evidence from a Prospective Birth Cohort Study". Here is the abstract:

It has been suggested that sleeping problems are causally associated with obesity in early life, but most studies examining this association have been cross-sectional. The authors used a population-based birth cohort of 2,494 children who were born between 1981 and 1983 in Brisbane, Australia, to examine the prospective association between early-life sleeping problems (at ages 6 months and 2–4 years) and obesity at age 21 years. The authors compared mean body mass indices (BMIs; weight (kg)/height (m)2) and persons in the categories of overweight (BMI 25.0–29.9) and obesity (BMI 30) among offspring at age 21 years according to maternally reported childhood sleeping problems. They found that young adult BMI and the prevalence of obesity were greater in offspring who had had sleeping problems at ages 2–4 years than in with those who had not had sleeping problems. These associations were robust to adjustment for a variety of potential confounders, including offspring sex, maternal mental health, and BMI, and several mediators, including adolescent dietary patterns and television-watching. These findings provide some evidence for a long-term impact of childhood sleeping problems on the later development of obesity.

So I hope you all get a good night's sleep!