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Chronobiologists all over the world agree, that clocks should follow natural time. Daylight saving time is an unnatural time and has serious consequences for physical and psychological health, especially if applied year-round [BTPK17, Dayl20, Kali00, RWSA19].

But why is that so?

Daylight saving time means living in a time zone that is too far east for the country's geographic location. The time of the day and consequently the social times, which we have to follow, are then too early for the actual position of the sun and therefore too early for our internal clock [RoWK19], which controls sleep and activity phases [KrMe13, S.4, 55, 68, 128]. Summer time thus shifts social times even further away from those that would be compatible with our internal clock, or in other words: we simply have to get up too early. The result is an increase in social jetlags [BTPK17]


Germany lives during daylight saving time with Eastern European time, thoughis lies geographically in the western part of Central Europe.

The acute problems that the clock change to summertime has are already known by most people.

The acute problems that the clock chance to daylight saving time has, is already known by most people.

However, the chronic consequences of a permanent life in the wrong time zone (permanent daylight saving time) are largely underestimated (see Myth "You get used to it.“). However, these are much more serious than the temporary acute problems of the clock change.

Acute consequences of the time change

Studies that look at the days after switching to daylight saving time show:

  • The night's sleep is shortened. [BaWa09]

  • Young people are more sleepy during the day. [ScRa09]

  • General accidents and visits to the emergency room increase. [FROF18]

  • Incidence of heart attacks increase. [JALM12, MFGZ00]

  • There are more strokes. [SRRK16]

  • Miscarriages occur more often after in-vitro fertilization. [LPCG17]

  • People suffer more from mood swings. [MoAp80]

The effects of the clock change are compared by scientists with those of shift work [MoAp80].

Chronic consequences of (permanent) Daylight Saving Time

Since daylight saving time increases social Jetlag [BTPK17], consequences of daylight saving equal the consequences of social jetlag.

(Permanent) daylight saving time

Myth: "You get used to it."

The underestimation of the risk behind permanent daylight saving time is based on the myth that the body adapts to it. It is scientifically proven, that the internal clock is not entrained by social times, but by light [Alle19, RoDM03]. The sun has a significant influence despite the existence of artificial light [Bori11, HBWC18, Rand08]. Average wake-up times follow the sun's east-west course in a time zone, even though the social time is the same [RoKM07]. It has been shown that cortisol rhythms (the “wakefulness hormone”) only advance two minutes during daylight saving time, even though the social clock has been changed by 60 minutes [HBWH14]. In Russia, there was a constant increase in social jetlag and a permanently increased level of winter depression during a 3-year long period of permanent daylight saving time (2011 - 2014) - effects that only disappeared when they returned to permanent standard time [BTPK17]. Activity profiles on weekends hardly react to the change to daylight saving time [KJMR07, RoKM07]. The nightly sleep is reduced by 19 minutes [GiMa19, Roen19]. Also, positive effects of the clock change in autumn back to standard time, such as " one hour more sleep", indicate a chronic lack of sleep [KlDi05, Roen19]. The fact that heart attack rates after the change to standard time in autumn sink [JALM12], suggests that they were increased during daylight saving time [RoWK19].

Another very obvious indicator that the sun has a big influence on which times feel better for our daily routines, is the fact that average working hours from east to west are getting later, as observed within the Central European Time Zone [RoWK19], even though the time on the clock is for everybody the same. In that way people try intuitively to protect themselves from the east-west delay of the solar time.

Earlier times for a late society? It doesn't make sense

Statistics show that the internal clock of most people is already "too late" compared the social norm. 93% need an alarm clock to get up at 6 a.m. [RPZW19]. This is shown by distributions of Chronotypes (sleep types) [RPZW19, SKAH20]. These people already suffer from social Jetlag [RPZW19]. Their body's sleep time does not meet the social norm. Or better said this way: the social norm does not meet the body's sleep times for most of the people.


Therefore, what sense does it make to set the social norm even earlier? This is exactly what summer time does.


Summer time means nothing more than having to get up an hour earlier. Instead of between 10 p.m. and 6 a.m., the statutory night's rest is in daylight saving time between 9 p.m. and 5 a.m. And that is too early. By choosing daylight saving time, we move social norms even further away from our natural sheep phases. Using daylight saving time as a new time standard, the population would then be made out of even later chronotypes, with an even more pronounced social jetlag  [BTPK17].

Particularly dramatic is a Daylight Saving Time in winter, as there our internal clocks are even later than in summer are due to the season [HBWC18, HBWH14, HNST18, KJMR07].

Debunked: Supposedly positive effects of Daylight Saving Time

Supposedly positive effects of daylight saving time, such as an increase in physical activity by one hour more light in the evening, are considered refuted [Roen19, Wats19, Zick14]. Studies show either only a very small increase in evening activity in some countries, no activity in other countries or even a decrease in activity [GPCI14, Roen19, Zick14].

The argument that an hour more light in the evening is good for health is also a misinterpretation of scientific data. It is true that we should enjoy as much daylight outdoor activities as possible. This sets our internal clocks. However, the time of the day at which we receive that light matters. With too little daylight, the internal clocks of most people get delayed and that contributes to social Jetlag [Roen19]. That is already the case for most people [RPZW19, SKAH20].But, in order to set our clock earlier and minimize this social jetlag, we need light in the morning [RoDM03] (see also light hygiene). And it is precisely this light in the morning that is taken away from us in daylight saving time. However, light in the evening, which daylight saving time gives us, delays our internal clocks even further, making our social jetlag even greater [RoDM03].

Myth: no-adjustment
Chronische Folgen Gesundheit
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