Energy is regulated by multiple systems — hormones, sleep, stress, blood sugar and nutrient status.

During perimenopause, several of these shift at once.

1. Hormonal Fluctuations

Oestrogen and progesterone begin to fluctuate unpredictably. Oestrogen supports:

▫️Energy regulation

▫️Mood stability

▫️Mitochondrial function (how cells produce energy)

When levels swing, energy can feel unstable.

Progesterone decline also affects sleep depth, which directly impacts daytime energy.

2. Sleep Disruption

Hot flushes, night sweats and 3am waking fragment sleep. Even if you are in bed for 8 hours, poor sleep quality leads to:

▫️Reduced deep sleep

▫️Impaired recovery

▫️Increased cortisol

Poor sleep alone can explain persistent fatigue.

3. Stress and Cortisol

Chronic stress raises cortisol. Short bursts of cortisol increase alertness. But chronically elevated cortisol eventually leads to:

▫️Mental exhaustion

▫️Reduced resilience

▫️Blood sugar instability

Perimenopause lowers stress tolerance, amplifying this effect.

4. Mood Changes

Low mood, anxiety and irritability are common during this phase.

Depression significantly affects energy levels.

If fatigue is paired with low mood, it’s important to explore this with a GP.

5. Blood Sugar Instability

Energy crashes often reflect glucose swings. If meals are:

▫️Low in protein

▫️High in refined carbohydrates

▫️Spaced too far apart

▫️Blood sugar rises and falls sharply.

Each crash triggers cortisol, creating that wired-but-tired feeling.

6. Loss of Muscle Mass

Muscle mass naturally declines with age. Less muscle means:

▫️Lower metabolic efficiency

▫️Reduced insulin sensitivity

▫️Lower physical energy capacity

Strength training directly improves this.

7. Nutrient Deficiencies

Fatigue can worsen if you are low in:

▫️Iron (especially ferritin)

▫️Vitamin B12

▫️Vitamin D

▫️Magnesium

Heavy periods during perimenopause can also reduce iron stores.

Blood testing is sensible before supplementing.

8. Lifestyle Load

Midlife often brings:

▫️Career pressure

▫️Caring responsibilities

▫️Emotional load

▫️Reduced recovery time

Your energy output may simply exceed your recovery input.