Jet lag, the pooled evidence and the authorised claim

Jet lag is not simple travel tiredness. It is the misalignment of the internal circadian clock with external time cues at the destination, which is why symptom severity tracks the number of time zones crossed rather than the duration of the flight. That physical distinction is essential because internal timing mismatches follow a precise direction and scale, whereas generalised fatigue does not. Travellers crossing time zones frequently turn to melatonin to assist the process, but the scientific literature and European consumer regulations define its role in distinct and specific terms.

What the pooled trial evidence revealed

A Cochrane review of 10 randomised trials in air travellers, airline staff and military personnel found that in 9 of the 10, melatonin taken close to the target bedtime at the destination, between 10pm and midnight, decreased jet lag after flights crossing 5 or more time zones. ^[1]

The extent of the benefit is not uniform across journeys. It is likely to be greater the more time zones are crossed, and less for westward travel, with the review reporting a calculation indicating that for every two travellers taking melatonin under these conditions, one experienced a reduction in symptoms that would not have occurred on placebo. ^[1]

Why intake timing dictates circadian adaptation

The review is explicit that the hour of intake matters. Taken at an unhelpful hour, early in the day, melatonin is liable to cause daytime sleepiness and delay adaptation to local time, which produces the opposite of the intended outcome. ^[1] Because melatonin acts biochemically as an internal darkness signal, introducing it into circulation at the wrong biological phase postpones the resynchronisation of central pacemakers.

CIBDOL · Why intake timing dictates circadian adaptation

Across the range of daily amounts evaluated the outcome was similar, with participants falling asleep faster and sleeping more soundly at the higher end compared to the lower end, and no additional benefit recorded above that range. A slow-release formulation was relatively ineffective, which the authors viewed as indication that a short-lived peak operates more successfully than a sustained flat release profile. ^[1]

Trip duration and adjusting the biological clock

Shifting the internal rhythm is not always the logical objective. For stopovers lasting one to two days a subsequent review advises against shifting the circadian system at all, since immediate adjustment is practically impossible, whereas for stays beyond four or five days it outlines timed exposure to and avoidance of light as primary methods to accelerate adaptation. ^[2] Attempting to reset cellular rhythms during brief transit periods imposes biological stress without providing functional utility.

Biological variation among individuals is substantial. Marked personal variations in the rate and direction of adjustment make aligning any schedule with an individual traveller's own circadian phase difficult, and differences in resilience against sleep loss during jet lag may relate to a length polymorphism in a human clock gene. ^[2] A schedule that proves manageable for one passenger can create sustained disruption for another.

European label claims and statutory wording

What a European food product label is permitted to state is considerably narrower than what the systematic review identified. The authorised claim covers the alleviation of subjective feelings of jet lag, with the word subjective constituting a mandatory part of the approved wording, and it can be displayed only in accordance with its specific conditions of use.

Under European regulations, the permitted statement character for character is:

Melatonin contributes to the alleviation of subjective feelings of jet lag

The inclusion of subjective reflects the regulatory focus on personal self-reported symptom scores rather than objective physiological clock shifts. A companion authorised claim governs sleep latency, specifying that:

Melatonin contributes to the reduction of time taken to fall asleep

Safety observations and product quality

The review notes that the incidence of adverse effects remained low, while case reports suggest two specific groups of individuals might encounter harm, one through an interaction with a prescribed medicine. It calls for both safety signals to be examined formally, and for regular pharmaceutical quality control of melatonin formulations to be instituted. ^[1] This article describes published research and quotes a regulation. It does not give medical advice, does not tell anyone what to take, and does not tell anyone when to take it.