I posted about a study a few months ago demonstrating that reduced steroidogenesis, and especially androgen synthesis, is a major cause behind so-called dry-eye disease, and restoring steroidogenesis by administering niacinamide (thus raising NAD+) reversed most of the pathology. The study below suggests that vitamin D may be able to achieve the same, and the mechanism of action is probably largely the same considering that vitamin D is crucial for steroidogenesis, and especially progesterone and androgen synthesis. It gets even better – vitamin D, being a (seco)steroid itself is known to be able to bind and activate several steroid receptors directly and thus may work even in the context of severe/irreversible steroid deficiency. More specifically, vitamin D has been shown to bind and activate the progesterone, androgen and thyroid receptors, all of which have demonstrated benefit for ocular health and dry-eye disease in particular.
https://doi.org/10.1016/j.clae.2024.102169
“…A new study published in the recent issue of Contact Lens and Anterior Eye journal found that supplementing with vitamin D (VD) may be a useful adjuvant therapy to reduce the symptoms and indicators of dry eye. DED is a prevalent ocular illness that affects 5 to 50% of people globally, according to estimates. Common ocular discomfort symptoms in DED include dryness, redness, a feeling of a foreign body, heaviness, light sensitivity, pain, discharge, itching, and eye strain. Also, the vitamin that has immunomodulatory and anti-inflammatory properties is vitamin D which was demonstrated by numerous studies to have a correlation between VD insufficiency and both the incidence and severity of dry eye disease (DED). In this meta-analysis, Zeying Chen and colleagues examined the symptoms and indicators of DED patients both before and after using VD supplements. The effectiveness of VD supplement in patients with DED published up to January 2023 was searched using four clinical trials registry websites (ISRCTN, ICTRP, CT, GCP, ICH) and ten databases (Cochrane, PubMed, Web of science, Embase, Ovid, CNKI, Scopus, CSTJ, SinomedWanfang). There were 8 investigations in all, comprising a total of 439 patients. In order to determine standard mean differences (SMD) for the Schirmer’s test (SH test), corneal fluorescein staining scores (CFSS, Oxford Scale, 0–5), tear film break-up time (TBUT), ocular surface disease index (OSDI), lid hyperemia, and visual analogue pain scale (VAS), two reviewers independently evaluated the quality of the literature and extracted data. The key finding of this study was that VD supplementation was found to be effective in reducing lid hyperemia (SMD −0.71, 95% CI −1.09, −0.32, p = 0.000), OSDI (SMD −1.10, 95% CI −1.45, −0.74, p = 0.000), and tear production (SMD 1.43, 95% CI 0.81, 2.05, p = 0.000) as well as tear film stability (SMD 1.19, 95% CI 0.83, 1.55, p = 0.000). Overall, this meta-analysis suggests that VD supplementation is an effective way to reduce several of the symptoms of DED, including lid hyperemia, TBUT, and SH test. Additionally, the subjective DED symptom score, OSDI, also improved. The subgroup analysis revealed that the oral version significantly improved when compared to the buccal spray and intramuscular injection”
