What the science says about magnesium, L-theanine, and more

When it comes to improving sleep, the supplement aisle (or amazon shopping page) can feel overwhelming. Magnesium, melatonin, valerian, L-theanine and dozens of herbal blends all promise “better sleep naturally.”

But what does the science actually say?

Here’s a look at the current evidence behind some of the most popular supplements for sleep.

1. Magnesium: Some Promise, but Mixed Results

Magnesium plays a role in muscle relaxation, nerve function, and stress regulation – all of which can influence sleep.

The research:

A 2021 meta-analysis of randomized controlled trials found that magnesium supplementation reduced the time it took to fall asleep by about 17 minutes, primarily in older adults with insomnia. However, it did not consistently improve total sleep time or overall sleep quality.

These studies were small, varied widely in dose and formulation, and had moderate-to-high risk of bias. So while there’s a modest signal of benefit, the evidence remains low quality and results are inconsistent.

A few smaller studies have shown possible improvements for people with diabetes, restless legs syndrome, or nocturnal leg cramps, but these are specific cases and not generalizable. The most common side effect is soft stools, especially with magnesium oxide. Look for well-absorbed forms such as magnesium glycinate or citrate, and avoid high doses.

Bottom line: Magnesium may help if you’re low in it or have trouble falling asleep, but it’s not a magic bullet.

2. L-Theanine and Magnesium: A Calming Combination?

L-theanine, an amino acid found in green tea, promotes relaxation by increasing alpha brain waves and calming the nervous system.

While there’s limited direct research on magnesium and L-theanine used together, a few studies on multi-ingredient blends (containing both) show promising results, including shorter sleep onset, better sleep efficiency, and improved next-day alertness.

However, since these formulas also contained other compounds (like tryptophan and tart cherry extract), it’s unclear whether the benefits come from the combination itself or the broader mix. More research is needed.

Takeaway: Magnesium and L-theanine may work well together for relaxation and sleep onset, but the science hasn’t yet proven a specific synergistic effect.

3. Other Supplements with Stronger Evidence

Some over-the-counter options are backed by stronger data for improving sleep:

    •    Melatonin: Reduces sleep onset time and improves sleep quality, especially for circadian rhythm disruptions (jet lag, shift work).

    •    Valerian root: Offers modest improvements in sleep quality and latency; generally well tolerated.

    •    Amino acids (tryptophan, L-theanine): Support relaxation and sleep continuity; tryptophan ≥1 gram appears most effective.

    •    Vitamin D and omega-3s: May support sleep if you’re deficient, though evidence is mixed.

    •    Herbal extracts such as chamomile, lavender, passionflower, lemon balm, and ashwagandha show potential in small studies, likely by enhancing GABA (a calming neurotransmitter) activity.

Magnesium and other nutrients may help some people, but effects are less consistent.

Summary: Melatonin, valerian, tryptophan, and L-theanine currently have the strongest evidence for improving sleep.

4. The Real Foundation: Behavior First, Supplements Second

Even the most effective supplement can’t replace the fundamentals of good sleep hygiene. Sustainable improvement comes from habits that support your body’s natural rhythms:

• Try to adhere to consistent sleep and wake times
• Move your body in a physically challenging way each day
• Limit caffeine, alcohol and large/heavy meals late in the day
• Reduce screen exposure before bed
• Create a relaxing wind-down routine
• Experiment with meditation, breathing exercises or other mindfulness practices

Supplements can play a supportive role, especially when used intentionally. But they’re not a substitute for the daily habits that restore and sustain your energy.

The Bottom Line

    •    Magnesium: modest benefit for falling asleep faster; limited effect on overall sleep quality

    •    L-Theanine: promotes relaxation and may complement magnesium, but data are limited

    •    Melatonin, valerian, and certain amino acids: strongest evidence for improving sleep quality

    •    Other supplements: may help if you’re deficient or under stress, but results vary

Final Reminder

Before starting any supplement, check with your doctor or a qualified healthcare professional, especially if you have health conditions, take prescription medications, or are pregnant or breastfeeding.

At Lasting Impact Wellness, we believe in sustainable, evidence-based approaches to health — supporting your body’s natural rhythms so you can perform, recover, and thrive for the long run.