The sea, the sun and our brain: what does science actually say?

Let's start with a molecule: DHA

DHA stands for docosahexaenoic acid. It is indeed an excellent word for Scrabble… but more importantly, it is an omega-3 fatty acid that is particularly important for our nervous system.

Our brain contains an enormous amount of lipids, and among them DHA holds a special place: it is found in high concentrations in the membranes of our neurons and in the structures involved in communication between nerve cells.

Why does this matter? Because a neuron does not function like a simple electrical wire. Its membrane is an extraordinarily dynamic structure, containing receptors, channels, proteins, and communication systems. And the lipid composition of that membrane influences how it functions.

DHA contributes in particular to the physical and functional properties of these membranes. It therefore plays a role in an environment that is essential to the transmission of information between neurons.

Is our brain really 'built with DHA'?

Partly, yes. But I prefer to say that DHA is one of the important structural components of the brain, because our brain is obviously not built from a single omega-3 alone.

It also needs proteins, glucose, cholesterol, iron, iodine, zinc, copper, vitamins, and many other nutrients. But DHA has a remarkable distinction: nervous tissue, and synaptic membranes in particular, are especially rich in it. And this becomes even more interesting when we look at brain development.

DHA is particularly important during pregnancy and the first years of life

A baby's brain develops at an extraordinary rate, and during this period it accumulates DHA in particular. This is especially important during the second half of pregnancy and the first years of life. DHA also plays an important role in the development of the retina.

This is why omega-3 needs, and DHA needs in particular, deserve special attention during pregnancy and breastfeeding. But this does not mean that just any supplement should be taken at just any dose: diet, individual needs, the quality of the supplement, and the medical situation must all be taken into consideration.

And now, let's go back a few million years

This is where the story becomes fascinating. The human brain is exceptionally well developed relative to our body mass, and building such a complex brain requires an enormous amount of energy and an enormous amount of nutrients.

A question has therefore long captivated researchers: what allowed our ancestors to gradually develop such a large brain? There is probably no single answer. Cooking food, access to more energy-dense foods, meat consumption, social interactions, language, cooperation, environmental pressures, and natural selection all likely played a role.

But there is also a particularly interesting nutritional hypothesis.

And what if access to water contributed to the expansion of our brain?

Some researchers have proposed that the exploitation of aquatic environments provided our ancestors with a particularly interesting combination of brain-essential nutrients: fish, shellfish, crustaceans, and lacustrine and coastal resources. These foods could supply preformed DHA, but also other nutrients important for neurological development.

And this is where a hypothesis was born: regular access to aquatic resources may have facilitated the expansion of the human brain. It is a scientifically interesting hypothesis. But a word of caution: we cannot say today that seafood created the human brain. Evolution is infinitely more complex.

Some scientists strongly support the aquatic DHA hypothesis. Others consider that the evidence does not allow us to demonstrate that a dietary intake of DHA from aquatic resources was indispensable to the increase in brain volume. Science is still debating this question, and that is precisely what makes it so fascinating.

But one thing is not really debated: DHA remains important for our brain today

We do not need to resolve human evolution to understand this. Our body can manufacture a certain amount of DHA from another omega-3 called ALA, found notably in certain plant-based foods. But this conversion is limited.

This is why direct dietary sources of EPA and DHA are of nutritional interest. The main sources include fatty fish (sardines, mackerel, anchovies, herring, salmon), certain seafood, and certain oils derived from microalgae.

An important clarification: algae and DHA

You often hear: 'Eat seaweed, it is rich in DHA.' That is a bit of an oversimplification. It is primarily certain microalgae that produce the DHA at the origin of the marine food chain, and fish then accumulate these omega-3s by feeding within that food chain.

Not all the algae you put on your plate therefore necessarily constitute a significant source of DHA. On the other hand, microalgae oils rich in DHA are now available, which represents a particularly interesting alternative to fish oils.

And now, let's talk about the sun

This is where we must be especially precise. Light is not merely something that allows us to see: our body possesses several biological systems that are sensitive to light.

The most obvious is our circadian system. The light received by our eyes informs our brain about the alternation between day and night, and thus contributes to the synchronisation of our biological clock. This clock influences sleep, alertness, body temperature, the secretion of certain hormones, and numerous metabolic processes.

That is why exposing ourselves to natural light in the morning can be particularly beneficial for our circadian rhythm.

But light can also act directly on our cells

And this is where a fascinating scientific field emerges: photobiomodulation. Certain wavelengths of red and near-infrared light can penetrate tissues, and our cells possess molecules capable of absorbing some of these photons.

One of the main targets being studied is found precisely in the mitochondria.

Back to the mitochondria

Mitochondria are often described as the "powerhouses" of our cells. This is a simplification, but a fairly useful one. They use energy derived from our nutrients to produce ATP, a kind of energy currency that can be immediately used by the cell.

Within the mitochondria, there is an enzyme called cytochrome-c oxidase, which participates in the mitochondrial respiratory chain. Experimental work shows that certain red and near-infrared wavelengths can influence this enzyme and several associated mechanisms.

This can alter mitochondrial function, ATP production, certain reactive oxygen species used as signals, intracellular calcium, and various cell signalling pathways. This is one of the things we study in photobiomodulation.

Does this mean that the sun "recharges" our mitochondria?

It is an appealing image. But scientifically, I would be far more cautious. We are not solar panels: our mitochondria produce their ATP primarily through nutrient metabolism and oxygen.

Red and near-infrared light can modulate certain mitochondrial processes under specific experimental and therapeutic conditions. That is not the same as saying "the sun supplies the energy for our cells." This distinction is fundamental.

And what about melanin in all of this?

Melanin is an extraordinary pigment. It contributes notably to determining the colour of our skin, hair and eyes. In the skin, it plays above all a major photoprotective role: it absorbs a portion of ultraviolet radiation and helps limit the damage it can cause to cells.

But today, far more extraordinary claims are circulating on the internet: that melanin is a battery, that it stores solar energy, that it converts light into energy usable by the body, that it functions as a semiconductor powering our metabolism.

We do not currently have the clinical evidence to present this as an established energy mechanism in human beings. Melanin has fascinating physicochemical properties and is the subject of a great deal of research. But moving from properties observed in biophysics to the idea that our skin constitutes a solar energy storage system would be going far too far.

So, sun or no sun?

Of course. Natural light is part of our biological environment. But as a physician, I feel strongly about this distinction: natural light does not mean uncontrolled sun exposure.

We need a normal alternation between light and darkness for our circadian system, and exposure to outdoor light in the morning is particularly beneficial for synchronising our biological clock. But this absolutely does not mean that we should seek excessive ultraviolet exposure.

Because UV rays cause DNA damage, premature skin ageing, precancerous lesions, and an increased risk of skin cancers. The biological benefit of light must never become a justification for sunburn.

And should one remove their sunglasses?

No, that is not a recommendation I would make as a general rule. To synchronise your biological clock, you do not need to look directly at the sun.

Go outside, walk, enjoy natural light. But never stare directly at the sun, and use appropriate eye protection when light intensity or circumstances require it. The retina has nothing to gain from dangerous exposure.

Should one eat fish?

For the majority of people, regularly incorporating dietary sources of omega-3s into a balanced diet is a reasonable nutritional strategy. Personally, I am particularly fond of small oily fish — sardines, anchovies, mackerel, herring — which provide EPA and DHA as well as other valuable nutrients.

The choice of fish is also important during pregnancy, notably in order to benefit from marine nutrients while limiting exposure to mercury found in certain large predatory species.

And should one take omega-3 supplements?

Not automatically. If your diet regularly provides you with sufficient EPA and DHA, supplementation is not necessarily essential. In certain situations, a supplement may be worthwhile, but I would not advise the entire population to arbitrarily take a high dose of fish oil simply to reach a number.

There is notably a biomarker called the Omega-3 Index, which measures the proportion of EPA and DHA in red blood cell membranes. A level around 8% or higher has been proposed in certain publications as being associated with a favourable cardiovascular profile. It is an interesting marker, but 8% is not currently a universal medical threshold that every person must absolutely reach. Once again: an interesting biomarker must not become a universal prescription.

And during pregnancy?

There, DHA deserves particular attention. The cerebral and retinal development of the foetus requires long-chain fatty acids, including DHA. Nutritional recommendations therefore place particular importance on an adequate intake of omega-3s during pregnancy and breastfeeding.

This can come from a suitable diet and, when necessary, from correctly chosen supplementation. But in a pregnant woman, as always, supplementation must take into account the overall diet and medical context.

In the end, did the sea build our brain and did the sun fuel it?

That is a beautiful phrase. But it is a little too beautiful to be entirely true. I would rephrase it as follows: aquatic resources probably constituted a particularly valuable source of nutrients necessary for brain development over the course of our evolution; and light is a powerful biological signal that influences our circadian clock and, at certain wavelengths, can modulate certain cellular and mitochondrial mechanisms.

Both of these phenomena are real. We simply do not need to turn them into an extraordinary theory for them to be fascinating.

Key takeaways

Your brain is extremely rich in lipids, and among them DHA, an omega-3, occupies an important place in neuronal membranes and in the development of the nervous system. Fish and certain aquatic resources are excellent sources of DHA, and their availability may have played a role in the evolution of the human brain — even if this hypothesis remains debated.

Natural light, for its part, is essential for synchronising our circadian rhythm, and certain red and near-infrared wavelengths can also influence mitochondrial function: this is the fascinating field of photobiomodulation. But this does not mean that we need to expose ourselves more to UV rays, that melanin works like a solar battery, or that an omega-3 supplement will increase the size of your brain.

I am Dr Florian Vallecillo, and if I had to sum all of this up in a single sentence: our brain probably carries part of the nutritional history of our evolution, and our body remains deeply synchronised with the light of our environment. So eat wisely, move outdoors, enjoy natural light, protect your skin from excessive sun exposure, and give your brain the nutrients it needs. And above all: let us not turn extraordinary science into extraordinary promises. Biological reality is already fascinating enough.