Brain Fog During Perimenopause: When the Neurotransmitters Responsible for Attention Lose Their Hormonal Support

Difficulty concentrating, forgetfulness, and struggling to find the right word are often attributed to mental load, fatigue, or age. The usual response is to slow down, make lists, and sometimes worry about memory loss.

These answers overlook a specific mechanism. The brain functions thanks to certain chemical messengers, and sex hormones support their production and action. When this support fluctuates and then decreases, attention wanders more quickly, information is retained less effectively, and words are harder to come by. This mechanism also depends on what the brain receives: energy, proteins, fats, and micronutrients.

‍

What does “mental fog” mean?

Brain fog, also known as mental haze, is not a disease. It is a set of symptoms: concentration wanes quickly, you walk through a room without knowing why, a familiar name is on the tip of your tongue, and it becomes difficult to follow a group conversation.

These complaints have one thing in common: attention. To memorize something, you must first perceive it. Information that hasn’t been taken in cannot be recalled, and what appears to be a memory lapse is often simply a failure to process the information. Acute stress acts at the other end of the chain: it can block the recall of information that was otherwise learned very well—such as a credit card PIN forgotten immediately after receiving bad news.

When a word doesn't come to mind, this relates to a related skill: verbal fluency—that is, the ability to quickly retrieve words and put them into sentences.

At what point do the capacities change?

A large-scale study by Inserm, the French public medical research institute, followed more than 7,000 people aged 45 to 70 for ten years, administering tests of memory, vocabulary, reasoning, and verbal fluency on three separate occasions.

The findings came as a surprise when they were published: performance began to decline as early as age 45, with vocabulary being the only exception. Among women, reasoning ability declined by 3.6% over a ten-year period in the 45- to 49-year-old age group, and by 7.4% in the 65- to 70-year-old age group.

In practice, maintaining cognitive function is therefore already a concern for women in the perimenopausal age group. And issues related to stress, fatigue, or mood are not permanent: once these causes are resolved, memory function returns. In fact, new neurons continue to form in the hippocampus—the region of the brain associated with memory—even in old age.

‍

Four Messengers to Reflect On

Attention and memory depend on four brain messengers called neurotransmitters.

• Norepinephrine, the messenger of alertness, attention, and concentration.
• Dopamine, the neurotransmitter associated with interest and motivation. It also determines what is worth retaining: only what seems important, moving, or rewarding makes it into long-term memory.
• Glutamate, which enables the encoding of new information.
• Acetylcholine, which consolidates memories in the hippocampus.

Intense, prolonged concentration depletes noradrenaline reserves, which are not fully replenished. The result of overexertion can be summed up in one sentence: you can no longer take in information, and you’re even less able to remember it.

These neurotransmitters also have their own internal clock. In the morning, norepinephrine and cortisol—the stress hormone—rise, helping us wake up. As the day goes on, their levels drop while serotonin—the neurotransmitter associated with calmness—takes over.

‍

How Hormones Change Things

Estrogens: Supporters of the Brain's Messengers

Estrogens act directly on the brain, which has receptors for them. They influence the production and release of serotonin, dopamine, acetylcholine, and GABA, the nervous system’s primary calming neurotransmitter. They also enhance serotonin and dopamine receptors.

Perimenopause occurs in two stages. Starting in one’s 40s, progesterone levels drop first, because ovulation becomes less regular. Then estrogen levels become irregular before declining. Each of these phases removes a source of support: progesterone has a calming effect, while estrogen has a stimulating effect on mood and motivation. When estrogen levels drop, noradrenaline and serotonin levels are affected, and attention suffers as a result.

DHEA, a hormone produced by the adrenal glands (two small glands located above the kidneys), stimulates the hippocampus and the formation of connections between neurons. Its levels decline with age, regardless of menopause. Finally, the decline in sex hormones is accompanied by an increase in oxidation (chemical wear and tear on cells) and inflammation, two factors that weaken neurons.

A brain that consumes a lot of energy

The brain accounts for only about 2% of body weight, but it alone consumes about 20% of the oxygen and energy derived from glucose. It is the body’s primary consumer of sugar, and it has no reserves of its own: it depends on a steady supply drawn from the liver’s reserves between meals.

Estrogens affect the secretion of insulin—the hormone that transports sugar into cells—and the cells’ sensitivity to its signal. Fluctuations in estrogen levels can therefore impact blood sugar regulation. Two to five hours after a meal that is too high in fast-acting sugars, a drop in blood sugar—known as reactive hypoglycemia—manifests as blurred vision, weakness, and mental fog.

As we age, mitochondria—the powerhouses of cells—function less efficiently, and neurons have a harder time absorbing glucose. Excess sugar exacerbates this decline: it promotes oxidation and disrupts the functioning of these very powerhouses.

Cut Out Carbs for a Clear Mind?

The experiment was conducted. Women followed either a low-carbohydrate diet or a balanced diet before taking tests. In the low-carbohydrate group, memory performance was poorer, but it improved as soon as carbohydrates were reintroduced. Alertness, on the other hand, was better in that group.

In practice, drastically cutting back on carbohydrates does not clear the mind: the brain needs a steady supply of glucose, which is provided by complex carbohydrates.

I will not discuss the ketogenic diet here, as it should be reserved for certain medical conditions and followed under medical supervision.

DHA, the building block of neural connections

Hormones aren’t the only factor at play: these messengers also need a carrier. DHA, a long-chain omega-3 fatty acid, accounts for about a quarter of the brain’s fatty acids on its own, and it is concentrated in the synapses—the points of contact between neurons. When it is lacking, dopamine, norepinephrine, serotonin, and acetylcholine are less effective at transmitting their signals. It also helps glucose enter the brain and stimulates a growth factor for neurons in the hippocampus.

‍

What Makes the Fog Thicker

Several factors come into play alongside hormonal factors. First, prolonged stress: excess cortisol weakens the hippocampus. In older adults who were followed for several years, persistently high cortisol levels were associated with a hippocampus that was 14% smaller and poorer memory performance.

Next, sleep, since it is mainly at night that memories are transferred to long-term memory. Long-term use of sleeping pills can itself impair memory.

Finally, iron, which is used to produce dopamine. In women who are still menstruating, an iron deficiency reduces dopamine and norepinephrine levels, and thus impairs attention. Vitamin B12 and iodine round out the list: a B12 deficiency can manifest as memory problems even before anemia develops, and an iodine deficiency increases attention problems.

‍

Nurturing Attention and Memory

The plate provides the materials these messengers need.

Protein spread out throughout the day

Dopamine and norepinephrine are produced from amino acids, the building blocks of proteins. Getting enough of them throughout the day is more important than the exact time of day they are consumed. The recommended daily intake during this period ranges from one gram to one gram and four per kilogram of body weight.

• A protein-rich breakfast, with eggs, tofu, nuts, or legumes. A sugary breakfast without protein can be counterproductive in the morning.
• Eggs, whose yolks provide choline, which aids in memory. Whether soft-boiled (four minutes), medium-boiled (six minutes), or poached (three minutes), they retain a runny yolk that protects their delicate fats. Hard-boiled eggs should be eaten in moderation. Choose eggs enriched with omega-3 (Columbus or Bleu-Blanc-Cœur).
• When practicing intermittent fasting, consume protein before 10 a.m.
• Complex carbohydrates late in the day, between 4:00 and 6:00 p.m., which promote serotonin production for the evening.

Small, fatty fish three times a week

• Sardines, herring, and anchovies are rich in DHA and low in pollutants, unlike large predatory fish.
• Gentle cooking methods: steaming, cooking in foil, marinating, or poaching with the heat turned off. Avoid frying.
• Canola, flaxseed, or camelina oils for seasoning, stored in a dark glass bottle in a cool place, as well as ground flaxseed and soaked chia seeds.
• Spinach in the same meal, with a drizzle of oil: its lutein, a protective pigment, is better absorbed when combined with fat. A study conducted on forty-nine women aged sixty to eighty found that verbal fluency was improved when DHA and lutein were taken together, rather than separately.

Slow-release carbohydrates, without cutting them out

• Legumes, whole grains, and sweet potatoes, which release glucose gradually.
• Start your meal with raw vegetables, and opt for starchy foods that have been cooked and then cooled, served as a salad, which lower the blood sugar spike by about one-fifth.
• Limit your intake of fast-acting sugars throughout the day, including at breakfast.

Polyphenols Every Day

Polyphenols are plant-based antioxidants that protect neurons.

• Berries: blueberries, strawberries, grapes. In older adults complaining of memory loss, twelve weeks of blueberry juice improved their ability to memorize lists of words. The trial was very small, but it paved the way for research in this field.
• Green tea, which contains theanine—a substance unique to tea—helps improve both concentration and mood while reducing stress response. Matcha and hojicha are two types of green tea. (Of Japanese origin; choose organic.)
• Dark chocolate with at least 74% cocoa, extra virgin olive oil, turmeric, thyme, and celery. Choose African-sourced ingredients to reduce exposure to cadmium.

Micronutrients for the Brain

• Magnesium, which helps regulate neuronal excitation: magnesium-rich water, oilseeds, and legumes.
• Vitamin B9, much of which is lost during boiling: eat raw green vegetables and herbs every day.
• Vitamin B12, which is found only in animal-based foods, should be monitored in those following a plant-based diet.
• Iodine is highly volatile: add iodized salt at the end of cooking, and eat seaweed in moderation.
• Vitamin D, the level of which is checked through a blood test.

The form and dosage of any supplements should be determined by your therapist or pharmacist.

Protecting Attention

• Get moving every day: walking, climbing stairs, tai chi. A study conducted on 120 people aged 55 to 80 showed that one year of regular walking increased the volume of the hippocampus by 2 percent, which is equivalent to reversing one to two years of aging.
• Avoid distraction: Constantly switching between tasks exhausts your brain's attention resources. Reducing noise and allowing yourself moments of calm helps you focus.
• Training Your Memory: Learn, Play, and Review Information Before Going to Sleep.
• Coffee in the morning—two to three cups at most—and none in the afternoon, to ensure a good night's sleep, during which memories are consolidated.

‍

Other Possible Causes

Thinking can also be clouded by other mechanisms, which often occur in addition to this one. Each is discussed in detail in a separate article:

• Sleep that no longer restores energy: see “Morning Fatigue.”
• Prolonged stress and cortisol: see “Hypersensitivity to Stress and Noise.”
• Iron deficiency or impaired cellular energy production: see “Energy Slumps.”
• An underactive thyroid: see “Weight Gain.”
• Sugar crashes in the late afternoon: see “Sweet and Salty Cravings.”

These causes are not mutually exclusive, and their combination is the rule rather than the exception.

‍

When to Seek Medical Attention

Seek immediate medical attention if you experience sudden confusion or difficulty speaking, deep sadness accompanied by a loss of interest or depressive thoughts, or memory problems combined with impaired coordination.

Seek medical attention if the brain fog persists, worsens, or interferes with daily life; if it is accompanied by fatigue, weight gain, hair loss, or dry skin; if you experience discomfort two to five hours after meals; or if you are taking long-term sleep aids, which should always be discontinued under medical supervision. This is something to discuss with your doctor, who can check your levels of vitamin B12, iron, vitamin D, and thyroid function.

‍

Key takeaways

Attention and memory depend on four brain messengers, several of which are supported by estrogen. During this time, that support fluctuates and then declines, while the brain—which is very energy-intensive—absorbs glucose less easily as we age. Stress, lack of sleep, and certain deficiencies in iron, vitamin B12, or iodine can make the brain fog worse.

These mechanisms explain why concentration wanes and why words are slow to come. They do not excuse inaction, and each person’s role involves taking concrete steps: spreading protein intake throughout the day, eating small fatty fish three times a week, consuming slow-release carbohydrates and polyphenols, engaging in daily physical activity, and minimizing distractions.

‍

Frequently Asked Questions

Is this the beginning of a memory disorder?

The “fog” described here primarily affects attention and the ability to process information, and it subsides once stress, fatigue, or mood disorders are overcome. However, if this condition steadily worsens or interferes with daily life, it should be evaluated by your doctor.

Why is it worse when I'm stressed?

Acute stress can block the recall of information that is otherwise well known, and prolonged stress depletes norepinephrine, the neurotransmitter associated with attention. A sustained excess of cortisol also weakens the hippocampus.