Why Your Sleep Changes After 40 — And the Nutrients That Help

If you slept like a rock in your twenties and now find yourself wide awake at 3 a.m. — staring at the ceiling with a busy mind — you are not imagining it. Sleep genuinely changes as we move through our late thirties and forties, and for many women the shift lines up with the hormonal transition toward perimenopause.

The good news: understanding why it happens makes it far easier to support your body gently, with routine and the right nutrients, instead of fighting it.

What actually changes after 40

Three things tend to happen at once:

• Deep sleep gets lighter. The proportion of slow-wave (deep) sleep naturally declines with age, so we wake more easily.
• Stress hormones stay elevated later. Cortisol, your primary stress hormone, is meant to fall in the evening. Modern stress — and shifting hormones — can keep it higher for longer, which works against winding down.
• Nutrient needs rise while intake often drops. Minerals such as magnesium are used up faster during periods of stress, yet many adults fall short of the recommended intake.

The magnesium connection

Magnesium is one of the most-studied minerals for relaxation and rest. It contributes to normal nervous-system and psychological function and to the regulation of the “calm-down” side of your nervous system. A 2025 randomized, placebo-controlled trial published in Nature and Science of Sleep followed 155 healthy adults reporting poor sleep and found that magnesium bisglycinate supported meaningfully better sleep scores over four weeks — with the strongest response in people whose dietary magnesium was below average (PubMed).

Why the form of magnesium matters

Not all magnesium is equal. Magnesium oxide is cheap but poorly absorbed and can upset the stomach. Magnesium bisglycinate — magnesium bound to the calming amino acid glycine — is a chelated, highly absorbable form that tends to be gentle on digestion, which is exactly why we chose it for our evening formula.

It is rarely just one nutrient

Sleep and stress are two sides of the same coin. That is why pairing magnesium with adaptogens like ashwagandha and calming compounds like L-theanine tends to make more sense than any single ingredient alone. We will go deep on each of these in this series.

Where to start tonight

• Dim the lights an hour before bed and keep screens out of the bedroom.
• Keep a consistent wake time, even on weekends.
• Support your intake of magnesium-rich foods — leafy greens, seeds, nuts, and dark chocolate.
• Consider a gentle, well-absorbed magnesium in the evening as part of a wind-down ritual.

Our Sleep + Stress 40+ formula brings magnesium bisglycinate together with KSM-66® ashwagandha and L-theanine — three research-backed ingredients designed to help you unwind and support restful sleep, your way.

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These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This article is for educational purposes only and is not medical advice. Consult your healthcare provider before starting any supplement, especially if you are pregnant, nursing, or taking medication.