Shift work has increased worldwide in recent years. Although this form of work has become an economic necessity, there are also significant health problems associated with it. Previous studies have already linked shift work to an increased risk of coronary disease with the highest risk associated with night shifts. Other related health issues include stomach ulcers, type 2 diabetes, and cancers such as prostate, colon, and breast cancer. Recent research shows that shift work can also delay the natural onset of menopause, possibly due to circadian rhythm disruptions.
Shift Work Interrupts the Circadian Rhythm
The body is synchronized to day and night by circadian rhythms – 24-hour cycles controlled by internal biological clocks that signal our bodies when to sleep, eat, and perform numerous physiological processes. However, people who work shifts have erratic sleep-wake patterns and mealtimes. The longer or strange working hours are not necessarily the problem. Instead, it’s the change in waking, sleeping, and eating patterns every few days that throws our body clock off balance, making it harder for it to maintain its natural 24-hour rhythm.
Although previous studies have shown the various adverse health effects of shift work on employed adults, there is little research on the effects of shift work on middle-aged and older adults. The age of natural menopause is a concern for middle-aged and older women, since both early and late menopause can be significant risk markers for later morbidity and mortality.
Later Onset of Menopause
Researchers have hypothesized that one factor that may affect a woman’s age when she enters menopause is shift work. Previous research has suggested a possible impact of circadian rhythm disruption on ovulation and fertility. To date, little has been documented about the link between shift work and the onset of menopause.
A study based on secondary data analysis from nearly 3,700 premenopausal women aimed to investigate the association between shift work and age variability in natural menopause in adult Canadian workers. Based on the study results, a significant association between changing shifts and a delayed onset of menopause was shown. Women who worked rotating or night shifts at any point in their lives were more likely to have had a higher age at onset of menopause compared to women who worked during the day. Women who worked rotating shifts at baseline were more likely to experience later menopause than day shift workers. Those who said they worked rotating shifts the most were more likely to be older at the onset of menopause than those who worked the longest hours of the day.
While the exact underlying mechanisms are not known, rotating shift work has been hypothesized to disrupt the circadian rhythm more than regular night work and has previously been studied as a risk factor for adverse reproductive outcomes. According to researchers, the delayed onset of menopause may be the result of circiadian disorders affecting estrogen production.
Shift Work and Heart Disease
Other research examined the association between shift work and risk factors for heart disease in female hospital workers who worked both shifts and off-shifts. The results of this study suggest that about one in five middle-aged women who do shift work have at least three risk indicators for heart disease. Of the women studied, 17 percent had metabolic syndrome with at least three of the identified indicators, and 38 percent had hypertension. Of particular concern was the finding that 60 percent of the participants had a waist measurement of more than 31 inches.
Belly fat and an increased waist size are good predictors of risk of heart disease, stroke, high blood pressure, high cholesterol and type 2 diabetes. The larger the waist measurement, the higher your risk of developing these conditions. The study found that age and current shift work status were significantly associated with an increased risk. Women over 45 who had reached menopause had a shift work history of over six years, and those currently working 12-hour or rotating shifts were more likely to have metabolic syndrome.
Irregular Working Hours Increase the Risk of Diabetes
Long-term rotating night shift work is an important risk factor for developing type 2 diabetes, and this risk increases with the number of years of rotating shift work. Women who work a rotating (irregular) schedule that includes three or more night shifts per month in addition to day and evening work hours that month may have an increased risk of developing type 2 diabetes compared to women who only worked during the day, according to a new study led by researchers at the Harvard School of Public Health (HSPH). In addition, the researchers found that longer years of rotating night shift work were associated with weight gain, which contributes to an increased risk of type 2 diabetes.
The researchers found that the longer women worked alternating night shifts, the greater their risk of developing type 2 diabetes. Those women who worked alternate night shifts for three to nine years had a 20% increased risk; somen who worked nights for 10 to 19 years had a 40% increased risk; and women who worked night shifts 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 follow-up. This study raises awareness of an increased risk of obesity and diabetes among night shift workers and underscores the importance of improving diet and lifestyle for the primary prevention of type 2 diabetes in this high-risk group.
Effects of Shift Work on the Brain
Shift work can also negatively affect the brain, according to research, leading to more severe ischemic strokes. The risk of a stroke increases significantly with age. Research has found that people who work shifts have a higher risk of severe stroke, both in terms of brain damage and loss of sensation and limb mobility. Interestingly, the study — supported by the American Heart Association — found that men and women differed greatly in the extent to which circadian rhythm disorders made stroke worse. In males, stroke severity in response to shift work schedules was much worse than in females. The researchers theorize that hormones could be to blame, as estrogen may have protective effects on the brain in women. However, older women approaching menopause showed an increasing incidence of ischemic stroke and a poor prognosis for recovery compared to men of the same age.
But how does shift work affect cognitive functions like memory and processing speed? Researchers tracked the cognitive abilities of more than 3,000 people who had either worked or retired in a variety of sectors at three points in time: 1996; 2001; and 2006. Just under half of the sample drawn from the patient lists of three occupational health practitioners in three different regions of southern France had worked shifts at least 50 days a year. The participants were exactly 32, 42, 52 and 62 years old at the time of the first series of tests, which aimed to assess long- and short-term memory. The data showed that those who currently or previously worked shifts had lower scores on memory, processing speed and overall brain performance than those who only worked normal hours. Researchers also looked at whether stopping shift work was associated with cognitive recovery. The results showed that it was possible to regain cognitive abilities after shift work ended, but it took at least five years, excluding processing speeds.
An immediate human health impact of these studies is that individuals in shift-work occupations should be monitored more closely and more frequently for cardiovascular and cerebrovascular diseases and risk factors such as hypertension and obesity. In addition, people who work shifts should pay special attention to a healthy diet, regular exercise, and consistent sleep.