Sleep: studies suggest that DHA resets the biological clock

The biological clock and circadian rhythms: what you need to know

The conductor of the sleep-wake rhythm

Our brain has a biological clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus. It governs our sleep-wake cycle.

In practical terms, it regulates our days, much like a natural clock. It gives signals to our nervous system to organise our waking and sleeping times and modulate our appetite.

These are known as circadian rhythms, which extend over a cycle of around 24 hours (1).

Regulating the biological clock: light and non-light triggers

The role of light

The biological clock regulates itself according to the alternation of day and night. It is determined by the light to which we are exposed.

Our eyes detect the intensity and colour of the light, then transmit the information to the central nervous system, which in turn adjusts the biological clock accordingly.

So, even when you travel to a country with a large time difference from your usual place of residence, it automatically adjusts to the new times of day and night.

This mechanism also explains why exposure to both natural and artificial light can make it easier to wake up or, on the contrary, harder to fall asleep (2).

But light is not the only factor that influences the way the biological clock regulates its functioning.

Non-light regulators

The regulation of the internal clock is also influenced by non-luminous stimuli (or non-photic zeitgebers) (3):

• physical activity, which can advance or delay the clock depending on the time of day
• mealtimes, which send signals to the body about the availability of energy and influence specific clock genes
• certain nutrients, which can directly or indirectly modulate the expression of genes regulating sleep-wake cycles (4)

Among the nutrients, omega-3 fatty acids, particularly of the DHA type, are thought to be powerful synchronisers, modulating our biological rhythms according to what we eat.

Studies explore the links between sleep and DHA consumption

Omega-3 fatty acids and sleep

There are two main types of omega-3 fatty acids: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

These are essential components of cell membranes, particularly in the brain, where they are involved in communication between neurons (5).

Recent scientific data shows that omega-3s, and DHA in particular, can influence the synchronisation of the circadian clock (6).

They act on the clock genes responsible for modulating circadian rhythms, but also on metabolic regulation, affecting hormone release and energy management.

These effects have been observed in both human and animal models.

A more specific role for DHA in sleep quality

A randomised controlled trial (7) highlighted a specific effect of DHA (but not EPA) on sleep quality in healthy adults.

Among participants in this study who took DHA, there was:

• an improvement in sleep efficiency, i.e. the proportion of time spent in bed actually devoted to sleep
• a reduction in the time taken to fall asleep
• a reduction in the fragmentation index, i.e. the number of awakenings during the night

The results therefore suggest that DHA not only helps us to fall asleep more quickly at bedtime, but also to stay asleep throughout the night.

Mechanisms of action and future prospects: the promising role of DHA

How could DHA promote good quality sleep?

As we have seen, research suggests that DHA acts on circadian genes.

These are the genes that regulate the sleep–wake cycle and coordinate many of the body's functions.

At the same time, DHA is a fatty acid that is incorporated into the membranes of our nerve cells.

This could influence communication between neurons and, indirectly, the production of melatonin and serotonin (8), two neurotransmitters.

Melatonin is the hormone secreted by our body to indicate to the nervous system that it is time to prepare for sleep.

It is also responsible for keeping us asleep throughout the night. It is therefore essential for regulating the biological clock.

For its part, serotonin is not only involved in the production of melatonin, but also in mood regulation (9), which can have an impact on how easily we fall asleep.

Increasing your intake of DHA could therefore help you to better synthesise these two hormones, indirectly influencing the sleep-wake cycle.

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Further research needed

Researchers are taking a close look at how DHA can affect our biological rhythms.

However, it is important to remain cautious. The results depend on a number of factors:

• the dose of fatty acids consumed
• the profile of the participants (age, state of health, basic diet)
• the duration of the clinical trials

Today, the data is still limited and needs to be confirmed by targeted, larger-scale research.

While DHA could well play a role in regulating sleep-wake rhythms, its use is only one avenue of research and not an established certainty.