Proline for restoring mitochondrial function in aging

A longevity superstar amino acid?

Proline is an amino acid that the body uses to make proteins. It is synthesized from the amino acid glutamate in a multistep process. We can also get proline from protein-rich foods, such as gelatin and collagen, which are particularly high in proline.

Proline in mitochondrial aging:

A 2024 study showed that proline is likely very important in healthy aging and may be able to restore mitochondrial function and ameliorate DNA damage in senescent cells. Mitochondrial dysfunction is thought to be one of the driving factors of aging and the decay of health.

Highlights from the study include that increasing proline levels in aging cells:

• induces mitophagy (the recycling of damaged mitochondria), which improves cellular energy production

• reduces senescent mesenchymal stem cells by promoting mitochondrial function

• mitigates DNA damage and inflammatory cytokine expression through its positive effect on mitochondrial function

The researchers found that proline levels are reduced significantly in senescent cells because glutamine is converted to urea instead of proline. They found that proline production could be restored by NANOG, a homeobox protein that acts as a transcription factor. Previous studies showed that NANOG could reverse cellular senescence in several cell types as well as restore and rejuvenate dysfunctional mitochondria. This new study shows that adding proline yields similar results. ¹

When the researchers restored the cellular proline levels, there was a significant improvement in mitochondrial function in the senescent stem cells and reversal of several of the signs of senescence.

Screenshot from the graphical abstract

Proline is synthesized in the mitochondria in a process involving NADP(H) and glutamate.² When NADP(H) is limited or glutamate is being used for other processes, proline synthesis is going to be limited.

Proline benefits: What do studies show?

There honestly aren’t that many studies involving just supplementing with L-proline (it isn’t a popular amino acid!). So these clinical trials are a mix of studies with just proline or with gelatin or collagen, which are high in proline.

Connective tissue production:

• A clinical trial involving 15g of vitamin C-enriched gelatin, which is high in proline, increased collagen synthesis.³

• A study in middle-aged men doing resistance training showed that 15-30g of vitamin C-enriched collagen increases connective tissue collagen synthesis and increases proline levels.⁴

Wound healing:

• A clinical trial using proline along with vitamin C, A, E, zinc and arginine showed significant improvements in hard-to-heal wounds in the elderly.⁵

Proline safety and possible side effects:

An animal safety study showed no observed adverse effects at 5% of the diet. That’s a lot of proline…. Injecting proline into rats at high levels for two weeks caused mild oxidative stress.

Metabolic modulation:
A study looking at the effect of glucose and proline on insulin, blood glucose, or glucagon levels showed that 1 mmol proline/kg lean body mass had little effect on those metabolic parameters. However, proline + glucose attenuated the rise in blood glucose levels compared to consuming 25 g of glucose alone, and it decreased the glucagon response.

In the brain:
At high concentrations due to rare genetic defects, proline can cause neurological problems, including seizures and psychosis. A new study showed that at very high concentrations, proline may act as a GABA mimetic. GABA is the inhibitory neurotransmitter, and high concentrations of proline inhibit glutamate decarboxylase. I’m not suggesting that dietary proline or a moderate proline supplement is going to raise proline levels enough to cause seizures, but I wanted to include this in case someone noticed a neurological change.

In cancer:
Higher proline biosynthesis is linked to the progression of cancer growth. If you have cancer, please talk with your oncologist before making any dietary changes or adding a supplement.

Where to get proline:

Food sources of proline include meat, fish, and dairy. However, skin and collagen are much higher in this amino acid than in muscle meat. Tofu is also a good source of proline.⁶

If you’re not eating ‘nose to tail’ and making delicious bone broth from grass-fed animal bones, you may want to consider trying supplemental proline. Again, gelatin and collagen are good sources, so that may be the route to go. With both gelatin and collagen, look for grass-fed beef and a reputable company. One that I like is this one.

Proline is also available as a stand-alone amino acid in powdered form or in capsules. I ordered it in powdered form, and the flavor is sweet with a bit of an odd aftertaste (easily hidden in a drink or yogurt). I’ve only taken it a couple of times, but it seems to give me vivid dreams along with good sleep. Could be coincidental. I’m also going to add some to my small patch of garden corn to see if it protects against stress (several good studies show that proline helps to protect against drought and salt stress).⁷

Conclusion:

The reversion of mitochondrial dysfunction in mesenchymal stem cells is intriguing. Research studies show that the individual amino acids affect health and longevity in multiple ways — some with a negative impact on insulin resistance and others with positive impacts. My bias may be coming through here - perhaps I like the idea of proline being beneficial because I think gelatin and bone broth are a healthy part of the diet.

1. Shahini, Aref, et al. “NANOG Restores the Impaired Myogenic Differentiation Potential of Skeletal Myoblasts after Multiple Population Doublings.” Stem Cell Research, vol. 26, Jan. 2018, pp. 55–66. ScienceDirect, https://doi.org/10.1016/j.scr.2017.11.018. https://www.sciencedirect.com/science/article/pii/S1873506117302489

2. Zhu, Jiajun, et al. “Mitochondrial NADP(H) Generation Is Essential for Proline Biosynthesis.” Science, vol. 372, no. 6545, May 2021, pp. 968–72. DOI.org (Crossref), https://doi.org/10.1126/science.abd5491. https://www.science.org/doi/abs/10.1126/science.abd5491

3. Shaw, Gregory, et al. “Vitamin C-Enriched Gelatin Supplementation before Intermittent Activity Augments Collagen Synthesis.” The American Journal of Clinical Nutrition, vol. 105, no. 1, Jan. 2017, pp. 136–43. PubMed, https://doi.org/10.3945/ajcn.116.138594. https://pubmed.ncbi.nlm.nih.gov/27852613/

4. Nulty, Christopher D., et al. “Hydrolyzed Collagen Supplementation Prior to Resistance Exercise Augments Collagen Synthesis in a Dose-Response Manner in Resistance-Trained, Middle-Aged Men.” American Journal of Physiology. Endocrinology and Metabolism, vol. 327, no. 5, Nov. 2024, pp. E668–77. PubMed, https://doi.org/10.1152/ajpendo.00252.2024. https://pubmed.ncbi.nlm.nih.gov/39259166/

5. Mehl, Adriano A., et al. “Hard-to-Heal Wounds: A Randomised Trial of an Oral Proline-Containing Supplement to Aid Repair.” Journal of Wound Care, vol. 30, no. 1, Jan. 2021, pp. 26–31. PubMed, https://doi.org/10.12968/jowc.2021.30.1.26. https://pubmed.ncbi.nlm.nih.gov/33439085/

6. https://tools.myfooddata.com/nutrient-ranking-tool/proline/all/highest

7. Khan, Pirzada, et al. “Proline Promotes Drought Tolerance in Maize.” Biology, vol. 14, no. 1, Jan. 2025, p. 41. PubMed Central, https://doi.org/10.3390/biology14010041. https://pmc.ncbi.nlm.nih.gov/articles/PMC11762158/