The most commonly linked deficiencies are iron, vitamin D, vitamin B12, zinc, folate, and sometimes biotin. Hair loss can also happen from too much vitamin A , so it’s not always just a “low vitamin” problem.

Quick Scoop

If you’re seeing shedding, thinning, or brittle hair , the deficiency most often checked first is iron , especially if you also have fatigue or heavy periods. Vitamin D and B12 are also frequently associated with hair loss, and zinc can matter too.

What to know

  • Iron deficiency : one of the most common nutrient-related causes of hair shedding.
  • Vitamin D deficiency : linked with alopecia areata and some types of thinning.
  • Vitamin B12 deficiency : can affect red blood cell production and scalp oxygen delivery.
  • Zinc deficiency : may contribute to thinning and poor hair growth.
  • Folate and biotin : sometimes discussed, but true deficiency is less common.
  • Vitamin A excess : too much supplementation can actually worsen hair loss.

When to get checked

If hair loss is sudden, patchy, severe, or lasting more than a few months , it’s worth asking a clinician about blood tests instead of starting random supplements. Hair loss often has multiple causes, so testing helps avoid missing things like thyroid issues, stress, or autoimmune conditions.

Bottom line

If you want the shortest answer: iron and vitamin D are the big ones most often associated with hair loss, with B12 and zinc also important.

If you want, I can also give you a simple list of blood tests to ask for.