The last Sunday of October proclaims the sombre call of winter with the ensuing hour loss of daylight as its dreary doleful echo. To compound our misery research now suggests that this clock change also incurs a significant threat to our long-term health.
For millions of years the endogenous body clocks of organisms have influenced life: anticipating our intraday activity patterns through diurnal fluctuations in rhythms of physiological, hormonal and behavioural processes. This includes our energy metabolism and especially our ability to handle glucose, which shows a pronounced diurnal rhythm with the highest tolerance seen upon waking, attenuating in the afternoon and significant impairment observed at night time [1].
It all suggests that it is early in the day when our bodies are primed for energy intake. And it makes sense too; that we consume energy during periods we are expected to be active i.e. early in the day and this need diminishes when we are at rest i.e. evening onwards. It seems the adage "breakfast like a king, lunch like a prince and dine like a pauper" is a practice worth cultivating. A good example is that of the night shift worker who demonstrates marked rises in plasma glucose and triglyceride levels in response to a standard meal, with shift work being associated with significant increases in obesity, coronary heart disease and diabetes [2, 3].
But, it is no longer just shift workers who need to be concerned about this increased risk. As the clocks go back it becomes more and more difficult to keep our endogenous clocks in sync with our exogenous environment. Our body clocks are synced by a light/dark cycle with the light exposure necessary to be of an intensity of 1000 lux or more (indoor lighting intensity is insufficiently bright, typically of a magnitude of 300-500 lux) meaning during the winter we experience less and less [1].
What we do get to experience though are shorter days with plenty of darkness, and in response to this there will be an increased conversion of the neurotransmitter serotonin to 'the night-time hormone' melatonin. Melatonin is a critical regulator of our biological clock signalling the night-time/rest period when caloric intake is deemed to be unnecessary. Thus, our tendency to eat our main meal in the dark evening is now misaligned with the rhythm of our biological clock. And what we find is that rises in our melatonin levels are associated with increases in insulin resistance, meaning that food consumed during this period has a dramatically increased propensity to cause the deadly triumvirate of obesity, diabetes and heart disease [4].
Couple this with the fact that this disruption to the normal alternation of our dark/light cycle produces a reduction in serotonin -also known as the feel-good happy chemical- which causes an increased craving for convenience sugar laden and junk food in a desperate bid to improve our mood (seasonal comfort eating), and it all leads to a maelstrom of weight gain and increased susceptibility to chronic disease.
The only way to ameliorate these deleterious effects is efforts to promote a better synchronisation with our body clocks. We can better align our body clocks to our diurnal activity through the non photic entraining stimuli of exercise and adopting improved eating habits [1]. This means that in the winter we have to go against our natural inclination to reduce our activity levels as its dark and miserable in the outside, as well as endeavouring to be more disciplined in our eating patterns -despite the encompassing festive season-, aiming to keep evening and night-time carbohydrate intake low, especially those of the simple variety e.g. white pasta, white bread, white rice, baked/roast potatoes, baked goods, soft drinks, desserts etc, to reduce insulin demand. For serious cases of rhythmic misalignment bright light therapy can also be used.
1.Kalsbeek, A., et al., The hypothalamic clock and its control of glucose homeostasis. Trends Endocrinol Metab, 2010. 21(7): p. 402-10.
2.Knutsson, A., Health disorders of shift workers. Occup Med (Lond), 2003. 53(2): p. 103-8.
3.Tucker, P., et al., Shiftwork and metabolic dysfunction. Chronobiol Int, 2012. 29(5): p. 549-55.
4.Morgan, L., et al., Circadian aspects of postprandial metabolism. Chronobiol Int, 2003. 20(5): p. 795-808.