Vitamin D

Vitamin D (most supplements are D3 / cholecalciferol) functions more like a hormone than a typical vitamin. After you take it (or make it from sunlight), it’s converted in the liver to 25-hydroxyvitamin D and then in the kidneys (and some other tissues) to calcitriol, the active hormone form. Calcitriol binds the vitamin D receptor (VDR) and influences gene expression across many systems—especially calcium/phosphate balance, immune signaling, inflammation, and aspects of mood/energy regulation. Because it’s hormonally active, dose and baseline level matter, and “more” isn’t always better.

In PFS/PSSD/PAS communities, vitamin D is often seen as a “basic” supplement, but there are still anecdotal reports of flares/crashes in some already-sensitized people—sometimes described as worsened anxiety, sleep disruption, fatigue, or sexual symptoms. The mechanism isn’t clear (and many people tolerate or benefit from correcting a deficiency), but a cautious, community-aligned approach is: check a 25-OH vitamin D lab first, start low, change one thing at a time, and stop if you consistently worsen, ideally with clinician guidance—especially if you’re also taking other hormone-active supplements.

Crash Anecdotes:

https://www.reddit.com/r/PSSD/comments/1ibo9hz/vitamin_d_i_feel_makes_my_symptoms_worse/

https://www.reddit.com/r/FinasterideSyndrome/comments/1alh3x1/vitamin_d/

My Personal Risk Ranking:

Low Risk of Permanent Worsening (for PFS/PSSD/PAS):
If you have PFS/PSSD/PAS, vitamin D is generally considered lower risk for permanent worsening, but some people still report symptom flares. When possible, sunlight exposure is a preferred way to support vitamin D. If you use supplements, consider a cautious approach: pause it and reintroduce it later (ideally after checking your level) so you can see clearly whether it affects your symptoms.