2. Hair loss
A hair loss that lasts for a long period may be a sign of vitamin D deficiency (5). If you are losing hair especially in the fall and winter when our body is less exposed to the sun, you may consider checking your vitamin D levels.
The thing is that the lack of vitamin D prematurely ages the hair follicles, making them unable to properly re-engage a new cycle of keratinization.
This factor would interact with the other factors of hair loss classically listed: heredity, stress, ferric anemia, thyroid problems …