Daylight saving time: what toll does it take on our bodies?

On the night between Saturday 24 and Sunday 25 October, the clocks will change: at 3 am, the clocks will go back one hour and it will be 2 am again. This will mark the reintroduction of standard time, which will remain in force until the last weekend of March 2027.

Standard time coincides with natural time. Days start earlier, because you gain an hour of daylight in the morning, but this also means they end earlier, as it gets dark sooner. People’s moods are often affected by this change. How often have you heard someone complain that, with darkness already setting in by mid-afternoon, they felt tired, sad or listless? Quite often. In some cases – particularly in those who are predisposed – this condition can contribute to the development of seasonal affective disorder, or SAD for short. The fifth edition – the most recent – of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) describes SAD as a recurrent major depressive disorder with a seasonal pattern. Its symptoms include irritability, a lack of energy and difficulty concentrating. These symptoms can also occur when the clocks change.

The main reason behind these symptoms is that changing the time – forwards or backwards – disrupts our biological clock. This clock ‘responds to light and the regularity of our routines. “The time change can temporarily cause drowsiness, waking up too early, irritability and difficulty concentrating,” explains Fabrizio Pregliasco, director of the Postgraduate School of Hygiene and Preventive Medicine at the University of Milan, past president of Anpas and vice-president of Samaritan International. When we switch to standard time, therefore, our bodies experience a mild form of jet lag: a bit like travelling to England. And this means that our bodies will have to resynchronise their internal rhythms with external ones. It is important to bear in mind that the circadian rhythm – that is, the biological clock – is regulated by melatonin. This hormone is produced by the pineal gland, which can take several days to adapt to the new timetable.

Among the most common symptoms – most of which have already been mentioned by Pregliasco – are chronic tiredness, a feeling of fatigue and a slight increase in cardiovascular stress. As Professor Carolina Lombardi – director of the Lombardy Sleep Medicine Centre – reports in her article, a study by Stockholm University indicates ‘a 4 per cent higher incidence of heart attacks in the week following the switch to standard time’. It should be emphasised, however, that this figure mainly affects older people.

The physiological disturbances associated with the time change are temporary and usually resolve ‘within about five days’, according to Luigi Ferini-Strambi, director of the Centre for Sleep Medicine at the IRCCS San Raffaele Hospital in Milan. However, prevention is better than cure. Therefore, in the days leading up to the switch to standard time, it may be helpful to adjust your meal and sleep times so that you reach the day in question with as little disruption to your routine as possible. In the days following the time change, experts suggest spending time outdoors and exposing yourself to natural light, which suppresses melatonin and helps to resynchronise your internal clock. As always, diet and physical activity can play a key role: the former to promote the body’s balance, the latter to relieve stress and combat low mood. People often turn to taking supplements as well. It is important that this is done on medical advice and that they are not overused, as virologist Pregliasco emphasises: ‘The time change is not, in itself, a reason to resort to supplements or sleep aids’. The final ‘tip’ is to make the most of the time change on the night between Saturday and Sunday, whether to catch up on sleep or to stay out an extra hour.