Shift Work, Insulin Resistance and Type II Diabetes:

Over the last week or so I’ve been immersing myself in online library data bases, scrolling through randomised clinical trials and observational studies, trying to find a link between shift work, insulin resistance and type 2 diabetes mellitus or T2DM.

Why would I do such a thing you may ask?  Well I may be a little crazy, but it begins with the letter ‘L’ , which stands for Literature Review, and in my case, I have a 2000 word Literature Review due this weekend.  Fortunately for me, I was able to choose a topic which I’m quite passionate about – that being shift work health.

However I have to say, what I’ve found in the depths of those data bases wasn’t exactly pretty.

So let’s talk firstly about working the night or evening shift.  Studies have shown an increased risk of diabetes in nurses who worked nights or evening shifts, which can be explained by a variety of different mechanisms.

1. Exposure to light at night leads to a decrease in the pineal release of melatonin, a strong antioxidant which plays a key role in the synthesis, secretion and action of insulin.  A reduction in melatonin has been associated with an increase in insulin resistance which over time, can lead to Type 2 Diabetes Mellitus or T2DM.
2. Persistent circadian stress as a result of disruption to the normal sleep/wake cycle, is common in night shift workers which may cause excessive secretion of cortisol (a stress hormone) and interleukins (proteins which are involved in the immune response).  These two things combined, along with an increase in insulin concentrations can lead to the build up of abdominal fat, lipid disorders and insulin resistance.
3. Working nights are often accompanied by changes in lifestyle, such as changing mealtimes which alters the timing of insulin response.

OK, now let’s talk about rotating shifts. 

1. It’s kind of obvious to anyone who has ever worked rotating shifts, that it’s really hard to adjust to a roster that is, for a better word – all over the place!  One minute we’re going to bed at 8pm to start work at 4am, and no sooner, 24 hours later we’re going to bed much later as we’re rostered on shift till midnight.  As a result it can be incredibly hard for the body to know when it needs to be sleeping and when it needs to be awake.
2. Studies have shown when exposed to continuous stress from trying to adjust as quickly as possible to varying work hours, the body becomes frustrated and struggles with the continual rotation of shifts.  Consequently, the health effects on these rotating shift groups may be more profound and pronounced than for other types of shifts.
3. Just working shift work places the body under biological stress (not to mention the physical and emotional aspects) which may lead to increased appetite, weight gain and glucose intolerance.  This in turn may contribute to the development of diabetes in shift workers.
4. Short sleep duration and poor sleep quality, which often represents the life of a shift worker, has been associated with psychological distress, higher levels of fasting insulin and inflammatory biomarkers, and a decrease in insulin sensitivity, which greatly enhances the risk of developing diabetes.

Does gender matter?

Now I don’t like to be sexist, but if you’re male, then you may be even more vulnerable to insulin resistance and T2DM than females.  This is because the diurnal patterns of testosterone levels are controlled by our circadian rhythms (our 24 hour body clock), and repeated disruption to this body clock may have an adverse affect on the male hormones.  In other words, shift work may influence androgen secretion (the male hormones) through regulation of the hypothalamic-pituitary-gonadal axis, which may contribute to a greater risk of T2DM in men as opposed to women.

So there you have it.  Not exactly a rosy picture for anyone who happens to work 24/7, but I think it’s important that every shift worker knows what they’re up against.  That way we can prioritise our health in a way that is going to help reduce the likelihood that we will develop endocrine disorders such as insulin resistance and type 2 diabetes mellitus later in life.

Stay tuned for my next blog post when I’ll talk specifically about which foods to eat that can help support glucose levels, thereby play a role in the prevention of developing disorders such as insulin resistance and type 2 diabetes.

References:

Hansen, A, Stayner, L, Hansen, J & Anderson, Z 2016, ‘Night shift work and incidence of diabetes in the Danish Nurse Cohort’, Occupational and Environmental Medicine, vol. 73, no. 4, pp. 262-268.

Gan, Y, Yang, C, Tong, X, Sun, H, Cong, Y, Yin, X, Li, L, Cao, S, Dong, X, Gong, Y, Shi, O, Deng, J, Bi, H & Lu, Z 2014, ‘Shift work and diabetes mellitus:  a meta-analysis of observational studies’, Occupational and environmental medicine, vol. 72, no. 1, pp. 72-78.