Although one must know that hair needs Protein ( Keratin) which is formed from Amino acids ( esp. L -Lysine), certain Vitamines ( Vit. A, Vit B6 B12, Biotin, Vit D and Vit E) and Minerals ( esp. Iron and Zink).
Dieting, Starving, Bariatric surgery ( for weight reduction) etc. can cause deficiency of one of these nutrients for the hair and can cause hair loss or growth problem. Although this is not common and esp. not in those who take regular balanced diet.
Deficiency should be diagnosed and can be treated by appropriate nutritional supplements. In females Iron deficiency is not uncommon due to monthly blood loss.
It takes 3-6 months before any change can be perceptible on regular treatment for deficiency correction. The miracle cures should be looked at with suspicion. There is no overnight cure.
The kind of picture that you have should be investigated for miniaturization studies and other tests to rule out Pattern Loss or other causes instead of simply taking vitamins. In fact excess of Vit A can cause other problems besides increasing your hair loss.