Slow Hair Growth

Nutritional deficiency
Brittle nails and slow-growing hair can also be an indicator of a nutritional deficiency. The national institutes of health report that approximately 20 percent of women have a common form of anemia caused by iron deficiency. One of the symptoms of iron deficiency anemia is brittle nails. Brittle nails, slow-growing hair, and lackluster skin can also be caused by a deficiency in omega-3 fatty acids or a deficiency in one of the b vitamins. The university of maryland medical center reports early studies suggest that supplements of biotin, one of the b vitamins, can improve brittle nails and hair loss.
Medication
If you’ve never suffered from brittle nails or slow-growing hair, and have recently started a new medication, you should consult your doctor or pharmacist to determine if this could be a side effect of your medication. Accutane, a medication prescribed to treat severe cystic acne, is just one of the prescription medications which lists brittle nails as a potential side effect for patients.
Genetics
If your mother, grandmother or other relative showed signs of brittle or thinning hair as they aged, you may find yourself genetically destined to following in their footsteps. Although you may not be able to completely avoid the problem, your doctor may be able to prescribe medication or supplements that can help improve your hair and nail condition.