Cancer Risk Increase
Three independent studies [Bori11a, GXDZ17, VWVH18] in different countries (USA, Russia, China) show:
Within a time zone, the risk of developing various types of cancer increases significantly from east to west. Additionally, life expectancy decreases with increasing west location [Bori11a].
The data used were standardized with regard to known cancer risk factors (smoking, age, socioeconomic status, overweight, latitude, urbanity, ethnicity, etc.).
Here are some values [GXDZ17]:
Every 5° geographical longitude further west - which corresponds to a sun delay of 20 min - increases the risk of
The reason for this? The further west one lives in a time zone, the higher the social jetlag [Bori11a, GXDZ17, VWVH18].
What does that mean in detail?
Let's imagine, Lisa, Ute, Oli and Tina live in cities with 100 000 inhabitants each, all in the same time zone, for example, in the United States in the Central American time zone (yellow area in picture). However, these cities are located in various east-west locations. Since they live in the same time zone, everyone's alarm clock rings at the same time, for example at 7 a.m.
But where Oli lives sun rises, due to the Earth's rotation, 20 minutes later than than in Tina’s City at the eastern border of the time zone. In Ute's city sunrise is another 20 minutes later than in Oli's city. In Lisa city sun rises another 20 minutes later than Ute's. The table shows the effect of this sun delay on the number of people who develop leukemia in a city of 100 000 inhabitants. While in Tina’s city there are 120 leukemia patients, there are in Oli’s city 135 (= 120 . 1.125), in Ute’s city 152 (= 135 . 1.125) and Lisa’s 170 (= 152 . 1.125). Where Max lives, sun rises even later than at Lisa’s place, but Max can sleep an hour longer because he already lives one time zone further (red area). When Lisa's alarm clock rings at 7 a.m., it is for Max only shortly before 6 a.m. When Max’s alarm clock rings at 7 a.m. (his time), the sun is rising. In his city there are as few leukemia cases as in Tina's city
Therefore, it is advantageous to live in the east of the (geographical) time zone..
Figure 1: Sun delay within a time zone. Source: [GXDZ17] edited.
Leukemia diseases per 100,000 inhabitants, based on an average leukemia risk of 1.5% [Leuk00].
What does that mean for Germany and Daylight Saving Time?
WRegarding cancer risk, during standard time, Germany is already not in an optimal position within its time zone, the Central European time, since it lies in its western half (see Fig. 1). Someone who lives in the east of Germany has already an increased risk of cancer compared to someone on the eastern edge of the time zone (for example in Warsaw). An eastern German citizen is located two times 20 minutes to the west (40 minutes). A western German citizen is three times 20 minutes further west (a full hour).
Figure 2: Germanys position in the Central European Time Zone (Standard Time).
However, it becomes really dramatic if Germany adopts the Eastern European time (daylight saving time) (see Fig. 2). Residents in eastern Germany would then be five times 20 minutes further west from the eastern boarder of the time zone (1h40 minutes), and residents in western Germany even six times 20 minutes (two full hours).
Figure 3: Germanys position in the Eastern European Time Zone (Daylight Saving Time).
What does that mean for Portugal and Daylight Saving Time?
With regard to the risk of cancer, Portugal is already not in an optimal location in its time zone, the Western European Time. Most of the territory even goes beyond the western edge of the time zone (see Fig. 4). The Portuguese are therefore at an increased risk of cancer compared to someone at the eastern edge of this time zone. They live more than three times 20 minutes further west.
Figure 4: Portugals position in the Western European Time Zone (Standard Time).
However, really dramatic is Portugal's position in the Central European Time Zone. This happens during daylight saving time (see Fig. 5). Residents in Portugal are in that case more than six times 20 minutes further west of the optimal location "Eastern edge of the time zone".
Figure 5: Portugals position in the Central European Time Zone (Daylight Saving Time).
Health-wise Portugal would have the best location its geographically correct time zone, the Azores Time Zone (see Fig. 6). It would be exactly on its eastern edge; the cancer risk would be the least of the three options mentioned.
Figure 6: Portugals position its geographically correct time zone, the Azores Time Zone.
For the archipelagos of Madeira and the Azores the situation is even less favorable. During standard time, the inhabitants of Madeira live about five times 20 minutes further west relative to the eastern end of their time zone (1h40m), as they have the same time zone as mainland Portugal. During summer time, they live eight times 20 minutes further west (2h40m), a discrepancy only bested by Galicia. For the inhabitants of Azores, during standard time, they live about four times 20 minutes further west (1h20m), relative to the eastern end of their time zone, Azores time. During summer time, this discrepancy becomes seven times 20 minutes further west (2h20m).
In terms of health, Madeira should adopt the time zone of the Azores, while the Azores should adopt the time zone UTC-2:00. It would be the case, to rethink the name of time zones to better represent the geographical areas that they should cover.