Week 2 Vitamin D nutrition, skin colour and cultural practices Flashcards
What is the ancestral human skin condition?
Dark skin with Africa as the birthplace of humans
- all humans had dark skin until relatively recently
- light skin colour migrated to high latitudes of europe of asia
- variation in skin pigmentation in all regions
Why is there variation in skin pigmentation within populations?
skin exposure and pigments
What causes skin pigmentation?
levels of:
- melanin
- melanocytes in the epidermis (skins outer layer) produce specific amounts and types of melanin
- carotenoids
How is skin colour determined?
genetically
What are the two major forms of melanin?
- pheomelanin is yellowish-reddish
- eumelanin is black-brown
How is melanin distributed?
different proportions in the skin and hair
- light skin mostly produce pheomelanin
- dark skin mostly produce eumelanin
Why is there different skin colour?
skin colour is an adaptation to UVR exposure
How is skin colour an adaptation to UVR exposure?
Result of multiple selective pressures:
- protects skin from cancer from UV radiation - darker skin is better
- prevents folate destruction from UV radiation - darker skin is better
- promotes vitamin D production from UV radiation - lighter skin is better
What is the geographic distribution of skin colour?
How does light vs. dark skin protect for skin cancer?
- dark skin heavily pigmented by melanin is better protected from skin cancer caused by exposure to UV radiation the lightly pigmented skin.
- light skin has about 10 fond risk of skin cancer compared to dark skin under same amount of exposure
death from melanoma and other skin cancers
what is a natural sunscreen?
melanin
What is folate?
a B vitamin
- froms RBCs and DNA synthesis, and developed the fetus nervous system
Whats food contain folate?
food sources include
- raw green leafy vegetables
- citrus fruits
- organ meats
- breads, cereals and pasta have fortified white flour with folate
What destroys folate and what protects it?
UV rays destroys folate but skin pigmentation can protect from it
- dark skin protects against the photodegradation of folate in the skins blood vessels
What does Vitamin D do?
vitamin D regulates intestinal Ca absorption, enables bone mineralization, and is needed for bone formation and remodeling
What does Vitamin D deficiency lead to?
- deficiency can cause rickets and osteomalacia and muscle aches
- suspected to cause asthma; autoimmune diseases such as rheumatoid arthritis, MS and IBS; diabetes and some cancers
what is rickets?
Bowed legs usually occuring in children because legs cannot support weight of child due to poor mineral absorbtion
What is osteomalacia, osteopinia and osteoporisis?
- osteomalacia: bones demineralizer and soften
- osteopinia: bone thinning
- osteoporosis: brittle bones
Natural foods containing Vitamin D3 and D2
D3
- fatty fish (salmon, sardines, herrings)
- fat of marine mammals (whale, seals)
- smaller quantities are in egg yolks
- organ meats (kidney and liver)
- red meat
- cheese
D2
- found in some plants and fungi (mushrooms)
- cows milk fortification
Who is at risk of vitamin D deficiency in terms of diet?
How is Vitamin D3 synthesized?
D3 is synthesized in the skin by the reaction of 7-dehydrocholesterol with solar UVB radiation
How does cutaneous production of Vitamin D3 change?
- photosynthesis of D3 in the skin changes with season, latitude, time of day, and the amount of pigment in the skin
- people 50 years or older have somewhat diminished capacity for cutaneous synthesis
- synthesis by UVB radiation only occurs year-round at latitudes between approx. 40N and 40S (Edmonton is 53 34’ N)
What skin pigment facilitates Vitamin D production?
- There was natural selection to promote vitamin D production through loss of melanin skin pigmentation under condition of generally low and highly seasonally variable level of UVBR
