If you have been diagnosed with telogen effluvium, or diffuse shedding without a clear cause, vitamin D is worth adding to the list of things to check. Research over the past decade has consistently found an association between low vitamin D and several types of non-scarring hair loss.
The Research Connection
A 2024 systematic review and meta-analysis published in Frontiers in Nutrition examined the relationship between vitamin D and non-scarring alopecias, including telogen effluvium, androgenetic alopecia, and alopecia areata. The review found an inverse relationship across these conditions: lower serum vitamin D was consistently associated with a higher likelihood of hair loss.
A separate case-control study on telogen effluvium found the difference was substantial. Patients experiencing telogen effluvium had a mean serum vitamin D level of roughly 13 ng/mL, compared to roughly 34 ng/mL in people without hair loss, a statistically significant gap. Other research has put the prevalence of vitamin D deficiency in telogen effluvium patients above 50%.
What This Doesn't Mean
None of this proves that low vitamin D causes hair loss on its own, and the research itself is careful about this distinction. The relationship could run in the other direction, or through a shared third factor. A review on the role of vitamin D in hair loss notes that while the association is well documented, conclusive evidence that vitamin D supplementation reverses hair loss is still limited. Vitamin D receptors are present in hair follicles and appear to play a role in the hair cycle, but the exact mechanism is still being studied.
Why Vitamin D Deficiency Is So Common
Vitamin D is unusual among nutrients because the body produces most of it through sun exposure on skin, not through diet alone. That makes deficiency common in people who spend most of the day indoors, live at higher latitudes, have darker skin (which produces vitamin D less efficiently from the same sun exposure), or consistently wear sunscreen, which is otherwise a good habit for skin health. The National Institutes of Health Office of Dietary Supplements estimates that a meaningful portion of U.S. adults have insufficient vitamin D levels, particularly in winter months.
What to Do About It
A blood test for 25-hydroxyvitamin D is the standard way to check your level, and it is worth requesting specifically if you are dealing with diffuse shedding and haven't had it checked. Levels below 20 ng/mL are generally classified as deficient, and 20 to 30 ng/mL as insufficient, though your provider may use different reference ranges.
If a deficiency is confirmed, correction usually happens through supplementation at a dose your provider recommends based on how low your level is, along with reasonable sun exposure where appropriate. Retesting after a few months gives you an objective way to track whether the correction is working, separate from what you can see in the mirror.
Hair loss rarely has one clean cause. Vitamin D is one of several nutritional threads worth pulling on, alongside iron, thyroid function, and overall protein intake, especially if standard bloodwork has come back "normal" and you are still shedding more than usual.
