[3] It provides extensive evaluation and treatment programs for children and adults with various metabolic bone diseases including osteoporosis, osteomalacia, stress fractures in young athletic women and men, and minimum trauma and nontraumatic fractures in infants, children and adults with hypermobility syndromes, Osteogenesis imperfecta, and Ehlers Danlos Syndrome.

[7] Holick made discoveries in the field of vitamin D that have led to novel therapies for metabolic bone diseases, hypocalcemic disorders, and psoriasis.

[17] He wrote several books about the importance of vitamin D and its beneficial health effects to the broad public, and discussed the benefits of sensible and the risks of excessive sun exposure.

[25] As a fellow, he participated in the first chemical synthesis of 1,25-dihydroxyvitamin D3[26] and 1α-hydroxyvitamin D3[27] to treat renal osteodystrophy,[28] hypoparathyroidism,[29][30] vitamin D dependent rickets type I,[31] and osteoporosis.

[42] He demonstrated that macrophages[43] and prostate cells[44] have the enzymatic machinery to produce 1,25-dihydroxyvitamin D3, and established that the extrarenal production of 1,25-dihydroxyvitamin D3 may play a crucial role not only in cancer prevention but also in regulating the immune system.

[48] He helped perform dose escalation studies establishing how much vitamin D is required to maintain blood levels of 25-hydroxyvitamin D in the sufficient range for adults.

He accepted research funding for this work from a non-profit tanning bed company, considered by many to be an important potential bias.