Could there be any permanent health effects form working 12 hour night shifts for 6 days in a row (10 pm to 10 am)? Especially on the brain?
This answer is more speculative than I like my answers here to be, but I think it still has some value.
It is highly unlikely that a single six-day period of working the night shift will have a permanent negative effect.
The problem is, this can't really be proven, and that is twofold.
First, pretty much all studies on the subject are either done on long-term effects on people who are working like this for a long time (shift workers), or they are done on people temporarily exposed to this, and with no follow-up on permanent effects.
Examples for the first type:
Circadian Rhythm Sleep Disorders: Part I, Basic Principles, Shift Work and Jet Lag Disorders - An American Academy of Sleep Medicine Review, a review on the effects of shift work on sleep
Is there an association between shift work and having a metabolic syndrome? Results from a population based study of 27 485 people - study on whether obesity and metabolic syndrome is more prevalent in shift workers
Examples for the second type:
Mistimed sleep disrupts circadian regulation of the human transcriptome - study measuring the short-term effects of delayed sleep on gene expression. No conclusions can be drawn for the long-term effects.
And second, this kind of study is also not really feasible. A lot of people go through a short or even medium term period of delayed sleep or even sleep deprivation in their lives. Think of, for example, students studying for exams not sleeping enough for a week or two. Patients receiving medication with the side effect of insomnia. Parents not sleeping enough for weeks, months, or even years. Teenagers partying late for several days in a row.
Getting a control group for such a study would be hard to impossible - I'd go as far as suggesting that by the time someone is 40 or 50 years old (so that we could compare long-term effects), almost nobody would even qualify as a control group subject who had never experienced sleep deprivation or delayed sleep for more than two days or so.
There are long-term effects of long working hours (12 hours is long) and shift work, but that is really another question and six days is unlikely to cause any of them.
Yes, working on night shift for six days surely may have permanent health effects. But it is very related to age, gender and some other conditions.
If it happens very rarely, effects will be probably mostly temporary. But if this happens often, effects may get to be permanent very easily.
But effects are very random. Two main effects will be higher blood pressure and wrong volume of hormones. Secondary effect may be that illnesses and conditions may get worse.
More information on:
... and there would be some other sources, but I could write only two - at this time.