Alertness on 12-hour night shifts
December 2, 2009
The problem with all night shifts, regardless of shift length, is that they don't match up with the lifestyles of the rest of the world. On nights, you are expected to be awake when everyone else is asleep and then you are to sleep when everyone else is awake. A pretty tall order.
Most shiftworkers on nights report getting less sleep than on any other shift. There are several reasons for this. First of all, if your circadian rhythms are set to keep you awake during the days and asleep at night, they will actually be working against you. Secondly, we don't like to sleep during daylight hours because we have family and social opportunities that we don't want to miss. Finally, there is the sleep environment itself. It is hard to completely isolate yourself from the lights and sounds of the day when you are trying to sleep.
All of this means we sleep less when working nights. The problem with 8-hour shifts is that there are a lot of them. This generally means that the more shifts in a row you work, the farther you fall behind in your sleep. At the same time, the more shifts in a row you work, the more able your body is to match your circadian rhythms to your new sleep pattern, thus improving sleep. So, on the one hand, more days in a row means more fatigue while, on the other hand, more shifts in a row means better sleep - eventually.
Now let's consider 12-hour shifts. There are a lot fewer shifts to work if you switch from 8-hour shifts to 12's. This generally means that you will only be working 2-4 night shifts in a row instead of 5-7 8-hour shifts in a row.
One popular schedule pattern is the 2-3-2. On this schedule, you work 2 or 3 nights in a row before getting a 2 or 3 day break. The good news is that you don't work too many nights in a row so you never fall too far behind in your sleep. The bad news is that since you work fewer nights in a row, you never get a chance to adjust to the shift. Additionally, you only have a few days off between shifts (on some patterns) which means you may have trouble readjusting to days (on your days off) as well.
If you go to a 4-on-4-off pattern, you will work more nights in a row and thus, fall farther behind in your sleep. However, the more nights in a row means (1) your body will adjust better to the night shift than if you worked fewer nights in a row and (2) more in a row means fewer times that you need to readjust to nights when you return to work and finally (3) you have 4 days off in a row which gives you a chance to adjust to days on your days off.
A 2-3-2 pattern means that you have to adjust to night shifts 78 times a year. A 4-on-4-off pattern only has 46 adjustments to nights in a year.
So, what is best for you? It comes down to your own behavior. If you find that you cannot adjust to nights at all, it is better to work fewer night shifts in a row to limit your accumulated sleep debt. If you adjust easily to nights, work more of them in a row to minimize those difficult first couple of days that we all go through when making the adjustment.