Vitamin D By Kristen Perrella

Source: https://online.epocrates.com/data_dx/reg/641/img/641-1-hlight.jpg

Biochemical Significance • Vitamin D3: formed from cholesterol skeleton by

ultraviolet radiation o Regulation of calcium and phosphorus metabolism

o Cholesterol7-dehydrocholesterol

• Rearranged by UV radiation from the sun cholecalciferol is

hydroxylated by liver enzymes to the most active form of vitamin D,

1,25-dihydroxycholecalciferol

• Active form of vitamin D, 1-25 dihydroxyvitamin D o Involved in cell death and survival pathways

o Depending on tissue, used in the protection of cells or in killing tumor cells

in conjunction with chemotherapy

Vitamin D pathway

Source: http://www.nutripeople.co.uk/userfiles/images/ANP-page-12.gif

Why Vitamin D is Important

Phosphorus Homeostasis

• Calcitriol acts on the same target organs as when maintaining calcium homeostasis to maintain phosphorus homeostasis

• Intestine

• Bone

• Kidneys

• Excess phosphorus is excreted in the urine in response to PTH

Cell differentiation, proliferation, and growth

• Within non-calcium regulating tissues, maintains normal cell growth, differentiation, and proliferation

• In some tissues, prevents malignancy by down-regulating cancer cell growth and inducing apoptosis as needed

• Treatment of psoriasis

Calcitriol and muscle

• Vitamin D deficiency

• Atrophy of type 2 (fast-twitch) muscle fibers

Vitamin D3 Deficiency: Rickets

• Nutritional disease o Bone malformation from improper calcium and phosphorus metabolism

o Deficient adults develop osteomalacia, a weakening of bone

o Childhood form of osteomalacia

• At risk: o People in areas with little sunshine (here!)

o People with darker skin color

• Melanin blocks some of the UVB rays

• Bowing of the legs

Source: http://en.wikipedia.org/wiki/File:XrayRicketsLegssmall.jpg

Sources of Vitamin D

Source: http://tasterie.com/blog/2012/03/vitamin-d-and-food-allergies/

Recommended Daily Allowance

• Assuming minimal sun exposure… o Children, adolescents, adults, including women who are pregnant or

lactating: 600 IU (15 micrograms)

o Age 70+: 800 IU (20 micrograms)

• During spring, summer, fall: o Try to get 5 to 15 minutes of sunlight between 10am and 3pm

Fair-skinned individuals generate 10,000 to 20,000 IU vitamin D in 15 to 30 minutes.

Current Research • DRI for calcium and Vitamin D from the IOM

o Prevalence of Vitamin D inadequacy has been overestimated

o 25-hydroxy vitamin D level—20 ng/mL / 600 IU vitamin D

• Need to reassess lab ranges to avoid problems of under-treatment and over-treatment

• Annual high-dose vitamin D and falls/fractures in older women o 500,000 IU cholecalciferol

• Prevent decreases in 25-hydroxycholecalciferol

o Autumn or winter

o Reduce risk of fractures and falls

o 2256 women, age 70+

o Resulted in an increased risk of falls

• 15% more falls

• 26% more fractures

References • Boyer, R. (2006). Concepts in Biochemistry (3rd ed.).

Hoboken, NJ: John Wiley & Sons, Inc.

• Gropper, S.S., Smith, J.L. (2013). Advanced Nutrition and Human Metabolism (6th ed.). Belmont, CA: Wadsworth.

• Ross, A.C., Manson, J.E., Abrams, S.A., Aloia, J.F., Brannon, P.M., Clinton, S.K.,…Shapses, S.A. (2011). The 2011 Report on Dietary Reference Intakes for Calcium and Vitamin D from the Institute of Medicine: What Clinicians Need to Know. Journal of Endocrinology Metabolism, 96(1), 53-58.

• Sanders, K.M., Stuart, A.L., Williamson, E.J., Simpson, J.A., Kotowicz, M.A., Young, D., & Nicholson, G.C. (2010). Annual high-dose oral vitamin D and falls and fractures in older women. Journal of the American Medical Association, 303(18), 1815-1822.