Rotating Night Shift Work Linked to Increased Risk of Type 2 Diabetes in Women, Study Finds

ScienceDaily (Dec. 7, 2011) — Women who work a rotating (irregular) schedule that includes three or more night shifts per month, in addition to day and evening working hours in that month, may have an increased risk of developing type 2 diabetes when compared with women who only worked days or evenings, according to a new study led by researchers at Harvard School of Public Health (HSPH). In addition, the researchers found that extended years of rotating night shift work was associated with weight gain, which may contribute to the increased risk of type 2 diabetes.


Previous studies have focused on the association between shift work and risk of cancer and cardiovascular disease. The HSPH study is the largest study so far to look at the link between shift work and type 2 diabetes and the first large study to follow women. The findings were published online Dec. 6, 2011 in the open access journal PLoS Medicine.

“Long-term rotating night shift work is an important risk factor for the development of type 2 diabetes and this risk increases with the numbers of years working rotating shifts,” said An Pan, research fellow in HSPH’s Department of Nutrition and the study’s lead author.

The researchers, led by Pan and senior author Frank Hu, professor of nutrition and epidemiology, analyzed data on more than 69,269 U.S. women, ages 42 to 67, in the Nurses’ Health Study I, tracked from 1988 to 2008, and 107,915 women, ages 25 to 42, in the Nurses’ Health Study II, tracked from 1989 to 2007. About 60% of the nurses performed more than one year of rotating night shift work at baseline; about 11% in Nurses’ Health Study I had more than 10 years of rotating night shift work at baseline, and about 4% in Nurses’ Health Study II worked more than 10 years of rotating night shifts at baseline, and this proportion increased during the follow-up.

The researchers found that the longer women worked rotating night shifts, the greater their risk of developing type 2 diabetes. Those women who worked rotating night shifts for three to nine years faced a 20% increased risk; women who worked nights for 10 to 19 years had a 40% rise in risk; and women who worked night shifts for over 20 years were 58% more at risk. In addition, women who worked rotating night shifts gained more weight and were more likely to become obese during the follow-up.

After taking into account body weight in the analyses, the increased risk of type 2 diabetes for women who worked rotating night shifts was reduced but remained statistically significant. For example, women who worked rotating night shifts for more than 20 years had 24% increased risk. These findings indicate that the relationship between night shift work and type 2 diabetes is partly explained by increased weight.

While the findings need to be confirmed in men and in some ethnic groups (96% of the participants were white Caucasians) and further studies are needed to identify underlying mechanisms for the association, the results are of potential public health significance due to the large number of workers who work rotating night shifts.

According to the U.S. Centers for Disease Control and Prevention (CDC), approximately 15 million Americans work full time on evening shifts, night shifts, rotating shifts, or other irregular schedules. Shift work has been shown to disrupt sleeping patterns and other body rhythms, and has been associated with obesity and metabolic syndrome, conditions associated with type 2 diabetes.

“This study raises the awareness of increased obesity and diabetes risk among night shift workers and underscores the importance of improving diet and lifestyle for primary prevention of type 2 diabetes in this high risk group,” said Hu. Studies also are needed to evaluate type 2 diabetes risk in other shift work schedules, such as evening shifts or permanent night shifts.

Support for this study was provided by the National Institutes of Health and career development awards from the National Heart, Lung, and Blood Institute.

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Moderate Alcohol Consumption Is Associated With Small Intestinal Bacterial Overgrowth, Study Finds

ScienceDaily (Oct. 31, 2011) — Just one drink per day for women — two for men — could lead to small intestinal bacterial overgrowth (SIBO) and subsequently cause gastrointestinal symptoms like bloating, gas, abdominal pain, constipation and diarrhea, according to the results of a new study unveiled at the American College of Gastroenterology’s (ACG) 76th Annual Scientific meeting in Washington, DC.

The retrospective review, “Moderate Alcohol Consumption is Associated with Small Intestinal Bacterial Overgrowth,” looked at the charts of 198 patients who underwent lactulose hydrogen breath testing (LHBT) to determine the presence of SIBO, and found that any current alcohol consumption was significantly associated with the presence of SIBO — and neither smoking nor use of heartburn drugs called PPIs was associated with an increased risk of SIBO.

Small intestinal bacterial overgrowth is a condition where abnormally large numbers of bacteria grow in the small intestine. Normally the small intestine contains a relatively low number of bacteria in contrast to the large intestine, which should contain a larger number of bacteria. In patients with SIBO, the abnormally large numbers of bacteria in the small intestine use for their growth many of the nutrients that would otherwise be absorbed.

As a result, a person with small bowel bacterial overgrowth may not absorb enough nutrients and become malnourished. In addition, the breakdown of nutrients by the bacteria in the small intestines can produce gas as well as lead to a change in bowel habits.

While previous studies have focused on alcoholics, who were found to have high rates of SIBO, this study by Scott Gabbard, MD and colleagues at the Dartmouth-Hitchcock Medical Center and the Mayo Clinic, is one of the first to look at the relationship between moderate alcohol consumption and SIBO. Moderate alcohol consumption means no more than 1 drink per day for women and 2 drinks per day for men, with twelve ounces of regular beer, 5 ounces of wine, or 1-1⁄2 ounces of 80-proof distilled spirits counting as one drink, according to the USDA dietary guidelines.

An overwhelming majority (95 percent) of the 198 patients in the study drank a moderate amount of alcohol, sometimes less than 1 drink per day, said Dr. Gabbard, who also indicated that only four of the patients drank more alcohol — a finding he noted indicates that consumption of even the slightest amount of alcohol could have an impact on gut health.

“These findings are significant because we now know that any bit of alcohol consumption–not just the amount consumed by alcoholics — is a strong predictor of a positive lactulose hydrogen breath testing and small intestinal bacterial overgrowth,” he said. “While typical treatment for SIBO has been antibiotics, probiotics or a combination of the two, the question now becomes what is the exact association between moderate alcohol consumption and SIBO and whether alcohol cessation can be used as a treatment for this potentially harmful condition.”

Starving Inflammatory Immune Cells Slows Damage Caused by Multiple Sclerosis, Study Finds

ScienceDaily (Sep. 1, 2011) — In a paper published in the journal Scientific Reports, a pair of researchers at the University of California, San Diego Skaggs School of Pharmacy and Pharmaceutical Sciences report that inhibiting the ability of immune cells to use fatty acids as fuel measurably slows disease progression in a mouse model of multiple sclerosis (MS).

MS is an autoimmune disease resulting from damage to the myelin sheath, a protective layer surrounding nerve cells. When the sheath is damaged, nerve impulses are slowed or halted, resulting in progressive physical and neurological disabilities. The cause of the damage is inflammation occurring when the body’s immune cells attack the central nervous system (CNS).

Marianne Manchester, PhD, professor of pharmacy and first author Leah P. Shriver, PhD, looked at how immune cells in the CNS oxidize fatty acids for energy when their preferred fuel source — glucose — is in short supply, which may occur in inflamed tissues. In a mouse model mimicking chronic MS, Manchester and Shriver discovered that by inhibiting a single enzyme that helps immune cells effectively exploit fatty acids, the cells eventually starved and died, preventing further inflammatory damage.

Currently, no approved drug or therapy for MS targets fatty acid metabolism. And the specificity of the target — inhibiting a single enzyme — suggests that adverse side effects associated with existing treatments, such as increased infection risk, is unlikely.

“We expect that because immune cells not in lesions in the CNS are able to use available glucose, they will function just fine during infection and that inhibition of this pathway would not produce general immune suppression,” Shriver said.

The enzyme-inhibitor used by Manchester and Shriver in their study is a drug already tested in humans with congestive heart failure, and was generally well-tolerated. The scientists are now using mass spectrometry to determine whether their results in the mouse model are translatable to humans. “We are interested in determining how this pathway is utilized in human tissue samples from MS patients,” Manchester said.

Funding for this study came from the National Institutes of Health and the National Institute of Neurological Disorders and Stroke.

Milk Better Than Water to Rehydrate Kids, Study Finds

ScienceDaily (Aug. 17, 2011) — Active children need to be watered with milk. It’s a more effective way of countering dehydration than a sports drink or water itself, say researchers at McMaster University.

That’s particularly important during hot summer weather, says Brian Timmons, research director of the Child Health and Exercise Medicine Program at McMaster and principal investigator of the study.

“Children become dehydrated during exercise, and it’s important they get enough fluids, particularly before going into a second round of a game. Milk is better than either a sports drink or water because it is a source of high quality protein, carbohydrates, calcium and electrolytes.”

He added that milk replaces sodium lost in sweat and helps the body retain fluid better. As well, the milk provides protein needed by children for muscle development and growth which is not found in the other drinks.

The study of eight to 10-year-olds involved exercising in a climate chamber, then receiving a drink and being measured for hydration.

Timmons, an assistant professor of pediatrics of the Michael G. DeGroote School of Medicine, said active children and adults usually don’t drink enough to stay hydrated during exercise, so they often have a “hydration disadvantage” when they start their next period of exercise.

He said that one per cent dehydration can have up to a 15 per cent decrease in performance, with an increased heart rate, core temperature and less ability to keep going. More significant dehydration comes with an increased risk of heat-related illness such as heat stroke.

Timmons’ graduate student Kim Volterman will be presenting the research at the European Group of Pediatric Work Physiology XXVII Biennial Conference, being held Sept. 19-23 at the University of Exeter in the UK.

Weight Gain Between First and Second Pregnancies Increases Woman’s Gestational Diabetes Risk, Study Finds

ScienceDaily (May 23, 2011) — Compared with women whose weight remained stable, body mass index gains between the first and second pregnancy were associated with an increased risk of gestational diabetes mellitus in the second pregnancy. But losing weight between the first and second pregnancies appeared to reduce GDM risk in a second pregnancy, particularly for women who were overweight or obese to begin with, according to a Kaiser Permanente Division of Research study appearing online in the journal Obstetrics and Gynecology.

GDM is associated with an increased risk of adverse perinatal outcomes as well as subsequent diabetes in women and their offspring, researchers say.

The study examined a diverse cohort of 22,351 women from Kaiser Permanente in Northern California over a 10-year period. Women who gained 2.0-2.9 BMI units (approximately 12 to 17 pounds) between the first and second pregnancy were more than two times more likely to develop GDM in the second pregnancy compared with those whose weight remained stable (plus or minus 6 pounds between pregnancies). Women who gained 3.0 or more BMI units (approximately 18 or more pounds) between the first and second pregnancy were more than three times more likely to develop GDM during the second pregnancy compared with those whose weight remained stable

Conversely, women who lost more than 6 pounds between the first and second pregnancy reduced their risk of developing GDM in the second pregnancy by approximately 50 percent compared with women whose weight remained stable. The association between losing weight and reduced GDM risk was strongest in women who were overweight or obese in their first pregnancy, explained the researchers.

Previous research has shown that excessive postpartum weight retention and lifestyle changes have been associated with a woman being overweight years after pregnancy, which increases the risk of developing non-insulin-dependent diabetes mellitus, said study lead investigator Samantha Ehrlich, MPH, a project manager at the Kaiser Permanente Division of Research in Oakland, Calif. Weight gain before pregnancy and gestational weight gain similarly have been shown to increase the risk of GDM. Additional research has shown that a pregnancy complicated by GDM is associated with a high risk of recurrent GDM in a subsequent pregnancy, explained Ehrlich, who is a PhD candidate in Epidemiology at the University of California at Berkeley.

This study is the first to examine whether weight loss before a second pregnancy reduces the risk of recurrent GDM.

Women who lose BMI between pregnancies appear to have a decreased risk of GDM in their second pregnancy, but there was significant variation by maternal overweight or obese status in the first pregnancy. Weight loss was associated with lower risk of GDM primarily among women who were overweight or obese in their first pregnancy, Ehrlich said.

She explained that being overweight or obese prior to pregnancy is a well-established risk factor for GDM. Women of normal weight who go on to develop GDM are likely to be more genetically susceptible to the disease. Thus, lifestyle changes resulting in weight loss may not be as effective in reducing GDM risk among normal weight women, she added.

“The results also suggest that the effects of body mass gains may be greater among women of normal weight in their first pregnancy, whereas the effects of losses in body mass appear greater among overweight or obese women,” Ehrlich said. “Taken together, the results support the avoidance of gestational weight retention and postpartum weight gain to decrease the risk of GDM in a second pregnancy, as well as the promotion of postpartum weight loss in overweight or obese women, particularly those with a history of GDM.”

In the study, BMI units were calculated for the average height of the study population, which was 5 feet 4 inches, and one BMI unit corresponded to approximately 6 pounds.

Co-authors on the study include Monique M. Hedderson, PhD; Juanran Feng, MS; Erica R. Davenport; Erica P Gunderson, PhD; and Assiamira Ferrara, MD, PhD, all with the Kaiser Permanente Division of Research in Oakland, Calif. The study was funded by a grant from the National Institute of Diabetes and Digestive and Kidney Diseases and a community benefit grant from Kaiser Permanente in Northern California.