L-Cysteine with Vitamin D and Blood Levels of Vitamin D
What it found
Taking L-cysteine alongside vitamin D may help the body make better use of vitamin D, according to lab and animal studies.
The authors say this combination could raise blood levels of 25(OH) vitamin D more than vitamin D alone.
What they found
Studies in people
Vitamin D deficiency is common
Nearly one billion people worldwide are deficient in vitamin D. In the US, nearly 45% of the population is deficient, and 70% of African Americans are deficient compared with 25% of white people.
Glutathione and vitamin D link
In healthy and diabetic people, blood levels of 25(OH) vitamin D and glutathione are positively linked. Obese children had lower levels of both than lean or overweight children.
Animal and lab studies
Combined supplement in animals
In mice fed a high-fat diet, giving vitamin D plus L-cysteine raised glutathione, turned on vitamin D-processing genes, and lowered oxidative stress more than vitamin D alone.
Lab studies on genes
In liver cells, blocking glutathione production lowered the activity of genes that convert vitamin D to its active form. Adding L-cysteine restored both glutathione and those genes.
Studies in people and animals
L-cysteine boosts glutathione
Supplementing with L-cysteine or N-acetyl-L-cysteine has raised glutathione levels in blood and tissues, and reduced inflammation and insulin resistance in both humans and animals.
Other findings
Suggested daily amounts
The authors suggest that a daily intake of 1000 mg of L-cysteine combined with 2000 IU of vitamin D may be a safer approach to raise blood vitamin D levels. They note that higher doses of L-cysteine can cause side effects like sleepiness, intestinal gas, and nausea.
What the authors conclude
“Therefore, it may be advisable to consider a daily intake of 1000 mg of LC combined with 2000 IU of VD as a potentially safer approach to elevate vitamin D levels in the bloodstream.”
Also in their conclusions
- They conclude that taking L-cysteine and vitamin D together is an innovative and better approach than high-dose vitamin D alone to raise blood levels of 25(OH) vitamin D.
- They advise that validation of this approach will lead to new clinical trials using L-cysteine with lower vitamin D doses to reduce vitamin D deficiency and its complications, especially in the African American population.
- They state that vitamin D supplements are unlikely to be successful unless glutathione status is also improved.
How it was done
Many people have low vitamin D levels even when they take high-dose supplements. The authors wanted to understand why vitamin D supplements often fail to raise blood levels enough to prevent chronic diseases.
The authors reviewed studies in people, animals, and cells that looked at how glutathione status affects vitamin D metabolism. They also examined how L-cysteine, a building block for glutathione, might improve vitamin D use when taken with vitamin D.
What it can’t tell you
- Most of the evidence comes from animal and cell studies, so it cannot show what happens in people.
- The review did not find any study that tested combined vitamin D and L-cysteine supplementation in people to see if it raises vitamin D levels or improves health.
- It is not known whether the suggested daily amounts of L-cysteine and vitamin D would work or be safe in the long term.
Who paid
- Funding
- Funded by NCCIH NIH HHS; NIH HHS (from the PubMed record).
- Conflicts
- The authors declare no conflicts of interest.
- Authors work at
- Louisiana State University Health Sciences Center, USA; Dell Medical School at the University of Texas at Austin, USA
The paper
- Title
- The Impact of Vitamin D and L-Cysteine Co-Supplementation on Upregulating Glutathione and Vitamin D-Metabolizing Genes and in the Treatment of Circulating 25-Hydroxy Vitamin D Deficiency
- Type
- ReviewThe authors read earlier studies and describe what they found. It isn’t a new study.
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Cite
- Jain SK, Justin Margret J, Abrams SA, Levine SN, Bhusal K (2024). The Impact of Vitamin D and L-Cysteine Co-Supplementation on Upregulating Glutathione and Vitamin D-Metabolizing Genes and in the Treatment of Circulating 25-Hydroxy Vitamin D Deficiency. Nutrients. doi:10.3390/nu16132004Free full textPubMed 38999752DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error