Researchers studied whether vitamin D and L-theanine (a compound found in green tea) could help older mice deal with stress and depression. The mice that received both supplements together showed big improvements in mood, energy, and how their brains worked. Their brains produced more dopamine (a chemical that makes us feel good) and had better electrical activity patterns. The combination worked better than either supplement alone. While this is promising research, it was done in mice, so scientists need to test it in people before we know if it will work the same way for humans.

The Quick Take

  • What they studied: Can vitamin D and L-theanine together help reduce depression and anxiety in older animals exposed to unpredictable stress?
  • Who participated: Aged laboratory mice that were exposed to chronic unpredictable mild stress to mimic depression in older adults
  • Key finding: Mice receiving both vitamin D and L-theanine together showed major improvements in mood and behavior, with brain dopamine levels nearly tripling and brain wave patterns becoming much more normal (2.33 times stronger alpha waves)
  • What it means for you: This research suggests that combining these two supplements might help with depression and stress in older people, but human studies are needed first. Don’t start taking these supplements without talking to your doctor, especially if you’re on other medications.

The Research Details

Scientists used older mice and put them through unpredictable stressful situations to create depression-like symptoms. They then gave some mice vitamin D, some L-theanine, some both supplements together, and some no treatment. They watched how the mice behaved (like how much they explored, played, or stayed still) and measured what was happening in their brains using special equipment that detects electrical activity and chemical levels.

The researchers used several different tests to measure depression and anxiety. They put mice in open spaces to see if they explored (anxious mice hide more), made them swim to see how hard they tried to escape (depressed mice give up faster), and offered them sugar water to see if they enjoyed it (depressed mice lose interest in things they normally like).

They also measured brain chemicals and electrical patterns directly from the mice’s brains to understand exactly how the supplements were working at a biological level.

This approach is important because depression in older adults is complicated—it involves multiple problems in the brain at the same time: low dopamine (the motivation chemical), too much oxidative stress (cellular damage), and poor communication between different brain regions. Testing a combination of supplements that might fix all three problems at once is smarter than testing single treatments. The researchers also measured brain activity patterns, which helped them understand the actual mechanism of how the supplements work.

This study was conducted in a controlled laboratory setting with careful measurement of outcomes, which is good for reliability. However, it was only done in mice, not humans, so results may not translate directly. The study appears to have used proper statistical analysis (P-values less than 0.05 indicate strong results). The researchers measured multiple outcomes (behavior, brain chemicals, and electrical activity), which strengthens confidence in the findings. The main limitation is that animal studies don’t always work the same way in people.

What the Results Show

Mice that received both vitamin D and L-theanine together showed dramatic improvements. They became more active and exploratory, spent more time in open spaces (suggesting less anxiety), and showed more interest in sweet things (suggesting improved mood). They also gave up less quickly when placed in water, meaning they had more motivation and energy.

The brain chemistry changes were striking. Dopamine levels—the chemical responsible for motivation, pleasure, and mood—nearly doubled in the treated mice compared to stressed mice. The brain’s electrical activity also improved significantly, with alpha wave patterns (associated with calm, focused attention) becoming 2.33 times stronger. This suggests the brain regions were communicating better with each other.

The combination treatment also boosted the brain’s natural defense system against cellular damage. Markers of oxidative stress (harmful cellular damage) dropped significantly, while protective antioxidant enzymes increased. This means the supplements helped the brain protect itself from damage caused by stress.

Importantly, the combination of both supplements worked much better than either one alone, suggesting they work together in complementary ways.

The study found that vitamin D and L-theanine appear to work through multiple pathways in the brain. They seem to improve the balance between GABA (a calming brain chemical) and glutamate (an activating brain chemical), which is important for reducing anxiety. The supplements also appeared to reduce inflammation in the brain and improve how brain cells communicate with each other. These multiple effects working together may explain why the combination was so effective.

Previous research has suggested that vitamin D deficiency is linked to depression, especially in older adults, and that L-theanine (from green tea) can promote relaxation. This study is novel because it’s the first to show that combining these two supplements together produces stronger effects than either alone in an aging model. The findings align with the growing understanding that depression involves multiple broken systems in the brain, and fixing multiple systems at once may be more effective than single treatments.

The biggest limitation is that this research was done in mice, not humans. Mice brains work differently from human brains in some ways, and what works in mice doesn’t always work in people. The study didn’t test different doses or durations of treatment, so we don’t know the optimal amounts or how long treatment needs to continue. The study also didn’t compare the supplements to standard depression medications, so we can’t say if they’re better, worse, or equal to existing treatments. Finally, the study was relatively short-term, so we don’t know about long-term effects or safety.

The Bottom Line

Based on this animal research, vitamin D and L-theanine show promise for helping with depression and stress in older adults. However, human clinical trials are needed before these can be recommended as a treatment. If you’re interested in trying these supplements, discuss it with your doctor first, especially if you take other medications or have health conditions. Current evidence suggests: Vitamin D supplementation may be reasonable if you have low levels (moderate confidence). L-theanine appears safe in the amounts studied (moderate confidence). The combination together is unproven in humans (low confidence).

This research is most relevant to older adults experiencing depression or anxiety, particularly those who don’t respond well to standard medications or who want to explore additional options. It may also interest people interested in natural approaches to mental health. People with vitamin D deficiency may particularly benefit. However, this should not replace professional mental health treatment. People taking blood thinners, those with kidney disease, or those pregnant/breastfeeding should avoid these supplements without medical approval.

In the mouse study, improvements appeared relatively quickly, but we don’t know how long it would take in humans. Based on other supplement research, if these work in people, you might expect to notice mood changes within 4-8 weeks, though some people might respond faster or slower. Mental health improvements typically take time, so patience is important.

Want to Apply This Research?

  • If your doctor approves trying these supplements, track your mood daily using a simple 1-10 scale, energy levels, and interest in activities you normally enjoy. Note any changes in sleep quality and anxiety levels. Record this weekly to spot trends over 8-12 weeks.
  • Start by getting your vitamin D levels checked by your doctor. If low, begin vitamin D supplementation at a doctor-recommended dose. Add L-theanine (typically 100-200mg daily) only after discussing with your healthcare provider. Use the app to set daily reminders to take supplements at the same time each day and log your mood immediately after.
  • Create a weekly mood and energy summary in the app. Compare your scores from week 1 to week 4, then week 4 to week 8. If you’re not seeing improvement by 8 weeks, discuss with your doctor about adjusting doses or trying other approaches. Continue tracking even if you see improvement to catch any changes. Share your tracked data with your healthcare provider at regular check-ins.

This research was conducted in mice and has not been tested in humans. These findings should not be used to replace professional mental health treatment or prescribed medications. Before starting vitamin D, L-theanine, or any supplement, consult with your doctor, especially if you are taking other medications, have existing health conditions, are pregnant or breastfeeding, or have a history of kidney disease. Some supplements can interact with medications or medical conditions. This summary is for educational purposes only and does not constitute medical advice. Always work with qualified healthcare providers for depression and anxiety treatment.