Why sleep shifts in your forties
Two things happen at roughly the same time. Deep slow-wave sleep — the physically restorative stage — declines steadily from your thirties onward. And in perimenopause, falling progesterone removes one of your body's own calming signals, while fluctuating estrogen destabilises the temperature regulation that a normal sleep cycle depends on.
The practical result is lighter sleep with more awakenings. That is a real physiological change, not poor discipline, and it responds better to consistent small adjustments than to any single product.
Magnesium glycinate
Magnesium supports GABA activity, the brain's primary calming neurotransmitter. Trials in older adults have found modest improvements in how quickly people fall asleep and how long they stay asleep, though the studies are small and the effect is not dramatic.
The form matters more than most people realise. Glycinate is well absorbed and gentle on digestion. Citrate works but has a laxative effect at higher doses. Oxide is poorly absorbed and is mostly what you find in cheap supplements. Typical study doses sit in the 200–350 mg range, taken about an hour before bed.
Magnesium is one of the few nutrients where a genuine dietary shortfall is common, so this is often correcting a deficit rather than adding a sedative.
Melatonin — and why less is usually more
This is the single most misunderstood item on the shelf. Your body produces roughly 0.3 mg of melatonin per night. Most retail products contain 5 or 10 mg — twenty to thirty times that.
Melatonin is not a sedative. It is a timing signal that tells your body night has arrived. Higher doses do not deepen sleep; they overshoot, leave residual melatonin circulating into the morning, and produce the grogginess people blame on the supplement itself. Research on low-dose melatonin has generally found 0.3–1 mg to be at least as effective as much larger amounts, with fewer next-day effects.
Melatonin also works best for timing problems — jet lag, shift work, a body clock that has drifted late. If your issue is waking at 3am, melatonin is usually the wrong tool.
L-theanine
An amino acid found in green tea. It increases alpha brain wave activity, the state associated with relaxed alertness, and reduces the mental churn that keeps people awake. It is not sedating, which is exactly why it suits people whose problem is a mind that will not switch off rather than a body that will not settle.
Studies typically use 100–200 mg. It has a good safety record and pairs well with magnesium.
Tart cherry
Montmorency cherry contains naturally occurring melatonin alongside anthocyanins that appear to influence tryptophan availability. Small trials in older adults have found modest increases in total sleep time. The effect is real but gentle — think of it as nudging rather than switching.
Glycine
Less discussed and genuinely interesting. Glycine lowers core body temperature slightly, which is one of the physiological triggers for sleep onset. Studies using 3 g before bed have reported better subjective sleep quality and less next-day fatigue. Worth knowing about if temperature regulation is part of your problem, which it often is in perimenopause.
Valerian
Popular, but the evidence is genuinely mixed. Some trials show benefit, others show nothing beyond placebo, and study quality varies widely. It also has a distinctive smell many people dislike. Not a bad option, but not the first one to reach for.
What the evidence does not support
Two honest caveats. First, no supplement outperforms the basics — consistent wake time, morning daylight, a cool dark room, and limiting alcohol in the evening all have stronger evidence behind them than anything you can buy. Alcohol in particular is worth singling out: it helps you fall asleep and then reliably fragments the second half of the night, which is precisely the half that goes wrong after 40.
Second, if you have loud snoring, witnessed pauses in breathing, or persistent daytime sleepiness despite adequate time in bed, that warrants a conversation with your doctor. Sleep apnoea becomes considerably more common in women after menopause and is frequently missed, because the classic presentation was described in men. No supplement addresses it.
A sensible starting point
If you are going to try one thing, magnesium glycinate has the best combination of evidence, safety and likelihood of correcting an actual shortfall. If racing thoughts are the main obstacle, add L-theanine. If your body clock has drifted, low-dose melatonin at 0.3–1 mg is the appropriate tool — not 10 mg.
Give any change three to four weeks before judging it. Sleep is noisy from night to night, and a single bad night tells you almost nothing.