A key aspect of hair loss with age is the aging of the hair follicle.  Ordinarily, hair follicle renewal is maintained by the stem cells associated with each follicle. Aging of the hair follicle appears to be primed by a sustained cellular response to the DNA damage that accumulates in renewing stem cells during aging.  This damage response involves the proteolysis of type XVII collagen by neutrophil elastase in response to the DNA damage in the hair follicle stem cells. Proteolysis of collagen leads to elimination of the damaged cells and then to terminal hair follicle miniaturization.
Most people experience some hair thinning as they age, but not everyone is affected to the same degree.
Men with male pattern baldness usually develop a receding hairline, hair loss at the crown, or both. Over time, men with hereditary hair loss can end up becoming completely bald.
Women with female pattern baldness, on the other hand, tend to develop thinning hair as opposed to total hair loss. This usually sees their hair become thinner across the scalp, especially at the hairline. The crown may be affected, but hereditary hair loss in women rarely proceeds to total baldness.
Deficiencies in nutrients such as vitamins A, E, D, iron, B vitamins and L-lysine may cause thinning eyebrows as well as thinning and weak hair. Fat-soluble vitamins A, E, and D all help to stimulate and support healthy hair growth and are found in spinach, carrots, bell peppers, kale, sunflower seeds, almonds, fish and eggs. Iron deficiency is diagnosed by measuring blood levels of ferritin and may be accompanied by frequent infections, brittle or spoon-shaped nails and decreased exercise ability. Sources of iron include meats, legumes, beans and whole grains. B vitamins are essential for metabolic functions in the body, and help the body cope with stress that can lead to hair loss. B vitamins are found in whole grains, leafy green vegetables, and legumes. L-lysine is an essential amino acid that appears to slow hair loss. Food sources include legumes, meat, fish, eggs, cheese and nuts. Therapeutic supplementation with the above vitamins requires consultation with a naturopathic doctor due to the potential for toxicity.