Previous research has indicated that nearly one-fifth of the US workforce engages in work outside the hours of 6 AM to 6 PM.1 These shift workers are more likely to work in lower-paying industries, including leisure and hospitality, arts and entertainment, mining, transportation, and warehouse work.1 In these industries, many workers are assigned either irregular or rotating shift work, further increasing the risk for circadian rhythm discordance.1,2

In a review published in the Journal of the American Osteopathic Association,1 Jay H. Shubrook, DO, of Touro University in Vallejo, California, and colleagues outlined current research on this topic and provided recommendations for how physicians can approach metabolic syndrome concerns in this patient population.

Risk Overview in Shift Worker Population

Multiple studies have demonstrated that shift workers are at an increased risk for metabolic syndrome,3,4 which leads to an increased risk for “the metabolic trifecta” of cardiovascular disease, stroke, and type 2 diabetes.1

“Initially, it was believed that unhealthy lifestyle choices and lower socioeconomic status were largely responsible for increased risk among this population, but the data do not support this belief,” according to the review by Dr Shubrook and colleagues.1 “For example, studies have found that night shift workers are not exercising less than the general population…[and] may even be exercising more than their day-shift counterparts.”

There is a growing body of research suggesting that circadian rhythm discordance is an independent risk factor for metabolic syndrome development.1 In shift workers, the circadian rhythm does not match the sleep-wake cycle, causing opposing signaling or circadian desynchrony. This desynchrony, Dr Shubrook and colleagues explained, disrupts the suprachiasmatic nucleus network rhythm, leading to disturbances in both sleep and metabolism.1 Some shift workers experience such significant circadian disruption that they develop shift-work sleep disorder, characterized by insomnia and the inability to stay alert at work.

In addition to circadian dysregulation, disturbances in hormone levels are common in this patient population, the review authors noted, and include increased cortisol and ghrelin and decreased thyroid-stimulating hormone, growth hormone, insulin, leptin, and serotonin.1,5-8 One study8 demonstrated that circadian desynchrony is specifically associated with decreased insulin sensitivity, a plausible explanation for worsened glycemic ranges present in shift workers.1

Hormonal cascades, linked to the development of metabolic syndrome, also have a reciprocal relationship with circadian rhythms.1 One rat-model study6 found that diet-induced insulin resistance led to circadian desynchrony; similar reciprocal relationships have also been noted with hormones like cortisol and melatonin and neurotransmitters including serotonin.1

“If a patient is found to meet the criteria for metabolic syndrome, a physician should thoroughly review all genetic, environmental, and behavioral factors that [might] contribute to the syndrome,” according to Rekha B. Kumar, MD, MS, assistant professor of medicine and attending endocrinologist at Weill Cornell Medical College and New York-Presbyterian Hospital. “Irregular sleep patterns, atypical mealtimes, and psychological stress at times of day that might not match one’s natural hormonal pattern of stress hormones can contribute to cardiovascular risk factors and metabolic syndrome.”

Recommendations: Assessment and Interventions

“Identifying any…irregular patterns related to one’s work schedule may help a physician make the connection between shift work and metabolic syndrome,” Dr Kumar noted. For physicians who are treating patients with metabolic syndrome, there are several clinical assessments and interventions available.

Promote sleep hygiene. “Sleep and circadian rhythm are very important to a healthy metabolism,” said Caroline M. Apovian, MD, director of nutrition and weight management at Boston Medical Center and professor of medicine at Boston University School of Medicine. Shift workers should aim to sleep in single, 7- to 8-hour blocks every 24 hours and should attempt to sleep as close to the same time of day as possible each day.1

In a sleep hygiene screening tool for shift workers,1 Dr Shubrook and colleagues suggest that physicians ask patients what their shift schedule is like, encourage patients to minimize rotating schedules, and suggest prophylactic naps where necessary. Physicians should also enquire about sleepiness during patients’ commutes, encouraging education about driver safety. Symptoms such as difficulty falling asleep, maintaining sleep, feeling tired while awake, feeling unrested after sleeping, headaches, difficulty concentrating, and slowed psychomotor coordination indicate a potential circadian sleep disorder.

With regard to the use of technology to help patients establish healthy sleep patterns, Dr Apovian suggested that such technology can be considered a useful tool for shift workers. Dr Kumar, on the other hand, suggested that these patients might benefit more from healthcare provider-guided support, adding that, based on patient preference, technology could be included as an adjunct to other structured lifestyle support.

Consider transitioning shift-work type. “[I]t is better to work night shifts consistently rather than switch between night and day shifts to avoid constant circadian rhythm disruption,” Dr Shubrook and colleagues note.1 However, if irregular shifts are unavoidable and a rotating schedule is common, 2 different transition techniques are available: night-to-morning to evening-to-night and night-to-evening to morning-to-night.1 Although some research indicates that the first option is associated with lower cortisol release, other research has found no significant difference between the strategies.1

Encourage use of workplace modifications. Physicians can suggest that patients take advantage of the following workplace modifications, if available1:

· Decrease blue light exposure by using the Redshift application for digital screens, installing lightbulbs that block blue light, and applying blue-light filters to head gear and eyewear

· Participate in health screenings covered by benefits, specifically yearly or biannual health screenings for metabolic syndrome and circadian desynchrony

· Engage in available health programs that promote healthy behaviors and provide incentives for employees to use health-tracking applications

· Take advantage of modified shift schedules to ease the burden of sleep debt and avoid rotating shift schedules

· Participate in modified break times, allowing for earlier meals and breaks at the same time each day

Recommend lifestyle modifications for nutrition and exercise. Despite the presumption that shift work is associated with lifestyle behaviors that increase the risk of developing metabolic syndrome, a 2016 meta-analysis found that night shift workers do not consume more calories than day shift employees.9 However, a reciprocal relationship between nutritional intake and circadian rhythm disturbance has been noted10 and should be addressed. Timing meals with activity cycles, for example, and maintaining regular eating patterns can reduce the development of obesity and metabolic syndrome,1 but night shift workers are “significantly more likely not to follow a daily eating pattern than those who work day shifts,”1,11 noted Dr Shubrook and colleagues.

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“Many patients who are shift workers cannot changes their jobs,” added Dr Kumar. “Addressing regular [eating] patterns is helpful and creating a structured routine to mealtimes, sleep time, and exercise are helpful in training the body to recognize a pattern and reduce physiologic stress.”

With that in mind, physicians should screen shift workers for disordered eating patterns and evaluate the nutritional quality of their food. Patients should be encouraged to eat 3 meals or more per day at similar times each day in order to decrease metabolic syndrome risk. In addition, these patients should be encouraged to eat more calories at the beginning of their wake cycle.1

For patients with a body mass index >25 kg/m2, Dr Apovian recommends the additional measure of encouraging the loss of 1 to 2 pounds per week through a healthy low-fat, low-carb diet and engaging in both resistance- and aerobic-based exercise. “If [the patient’s] blood glucose is high, think about [adding] metformin [therapy] for the reduction of body weight and pre-diabetes treatment,” Dr Apovian added.

To manage nutrition, Dr Kumar also suggests working with patients to develop a schedule that strategically times breakfast, snacks, sleep, and exercise.

“I…create a schedule that involves breakfast — usually in the morning coming off their shift — sleeping a several-hour stretch at the same time each day…regular exercise time, a meal before they start their shift, and 1 to 2 snacks during their shift,” she wrote.

In addition to mindful nutrition practices, physical activity in particular can reestablish a patient’s circadian rhythm and decrease inflammation in shift workers. Physicians should help shift workers develop a physical activity plan that is feasible with the patient’s work schedule, while keeping in mind recommendations that these patients should attempt to exercise at a similar time each day, at least 5 hours before going to bed.1

Suggest pharmacologic interventions where appropriate. Medications may be helpful in promoting circadian balance and “[a]nything that can affect hormone equilibrium can be beneficial to patients with metabolic syndrome,” Dr Shubrook and colleagues wrote. Using pharmacologic interventions to regulate both sleep and wake cycles can benefit metabolic disorders.1

Melatonin is one such possible pharmacologic intervention, the use of which promotes phase shift advance and has been demonstrated to improve sleep onset, efficiency, and duration. However, excess melatonin dosing can lead to worsened sleep cycles.1 Melatonin may be purchased over the counter as pills, liquid drops, or sublingual tablets.

Conclusions

It is essential to identify circadian discordance in shift workers as early as possible in order to reduce the risk for development of metabolic syndrome. In this population, primary prevention through lifestyle modification is “the best way to address both the quality of life and the long-term healthcare burdens” that shift workers experience.1

Clinical trials must also be conducted to evaluate both clinical and workplace interventions for shift workers. “[F]uture research on the influence of lifestyle factors and pharmaceutical interventions should be done to determine the most effective strategy to reduce the burden of metabolic syndrome in this population,” Dr Shubrook and colleagues concluded.1

References

1. Kulkarni K, Schow M, Shubrook JH. Shift workers at risk for metabolic syndrome. J Am Osteopath Assoc. 2020;120(2):107-117.

2. McMenamin TM. A time to work: recent trends in shift work and flexible schedules. United States Bureau of Labor Statistics Monthly Labor Review. December 2007. https://www.bls.gov/opub/mlr/2007/article/time-to-work-recent-trends-in-shift-work-and-flexible-schedules.htm

3. Proper KI, van de Langenberg D, Rodenburg W, et al. The relationship between shift work and metabolic risk factors: a systematic review of longitudinal studies. Am J Prev Med. 2016;50(5):PE147-E157.

4. Pan A, Schernhammer ES, Sun Q, Hu FB. Rotating night shift work and risk of type 2 diabetes: two prospective cohort studies in women. PLoS Med. 2011;8(12):e1001141.

5. Challet E. Keeping circadian time with hormones. Diabetes Obes Metab. 2015;17(suppl 1):76-83.

6. Touati H, Ouali-Hassenaoui S, Dekar-Madoui A, Challet E, Pévet P, Vuillez P. Diet-induced insulin resistance state disturbs brain clock processes and alters tuning of clock outputs in the Sand rat, Psammomys obesus. Brain Res. 2018;1679:116-124.

7. Morris CJ, Purvis TE, Mistretta J, Scheer FA. Effects of the internal circadian system and circadian misalignment on glucose tolerance in chronic shift workers. J Clin Endocrinol Metab. 2016;101(3):1066-1074.

8. Qian J, Dalla Man C, Morris CJ, Cobelli C, Scheer FAJL. Differential effects of the circadian system and circadian misalignment on insulin sensitivity and insulin secretion in humans. Diabetes Obes Metab. 2018;20(10):2481-2485.

9. Amani R, Gill T. Shiftworking, nutrition and obesity: implications for workforce health—a systematic review. Asia Pac J Clin Nutr. 2013;22(4):698-708..

10. Potter GDM, Cade JE, Grant PJ, Hardie LJ. Nutrition and the circadian system. Br J Nutr. 2016;116(3):434-442.

11. Sudo N, Ohtsuka R. Nutrient intake among female shift workers in a computer factory in Japan. Int J Food Sci Nutr. 2001;52(4):367-378.