Do subjective symptoms predict our perception of jet-lag?

A total of 39 subjects were studied after a flight from the UK to either Sy dney or Brisbane (10 time- zones to the east). Subjects varied widely in th eir age, their athletic ability, whether or not they were taking melatonin, and in their objectives when in Australia. For the first 6 days after arri val, subjects scored their jet-lag five times per day and other subjective variables up to five times per day, using visual analogue scales. For jet-l ag, the scale was labelled 0= no jet-lag to 10= very bad jet-lag; the extre mes of the other scales were labelled -5 and +5, indicating marked changes compared with normal, and the centrepoint was labelled 0 indicating `normal '. Mean daily values for jet-lag and fatigue were initially high (+ 3.65 +/ - 0.35 and + 1.55 +/- 0.22 on day 1, respectively) and fell progressively o n subsequent days, but were still raised significantly (p <0.05) on day 5 ( fatigue) or day 6 (jet-lag). In addition, times of waking were earlier on a ll days. By contrast, falls in concentration and motivation, and rises in i rritability and nocturnal wakings, had recovered by day 4 or earlier, and b owel activity was less frequent, with harder stools, on days 1 and 2 only. Also, on day 1, there was a decrease in the ease of getting to sleep (-1.33 +/- 0.55), but this changed to an increase from day 2 onwards (for example , + 0. 75 +/- 0.25 on day 6). Stepwise regression analysis was used to inve stigate predictors of jet-lag. The severity of jet-lag at all the times tha t were measured was strongly predicted by fatigue ratings made at the same time. Its severity at 08:00 h was predicted by an earlier time of waking, b y feeling less alert 30 min after waking and, marginally, by the number of waking episodes. Jet-lag at 12:00 and 16:00 h was strongly predicted by a f all of concentration at these times; jet-lag at mealtimes (12: 00, 16: 00 a nd 20:00 h) was predicted by the amount of feeling bloated. Such results co mplicate an exact interpretation that can be placed on an assessment of a g lobal term such as jet-lag, particularly if the assessment is made only onc e per day.