Week 2 Vitamin D nutrition, skin colour and cultural practices

Question 1

What is the ancestral human skin condition?

Answer 1

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

Question 2

Why is there variation in skin pigmentation within populations?

Answer 2

skin exposure and pigments

Question 3

What causes skin pigmentation?

Answer 3

levels of:

• melanin
  
  • melanocytes in the epidermis (skins outer layer) produce specific amounts and types of melanin
• carotenoids

Question 4

How is skin colour determined?

Answer 4

genetically

Question 5

What are the two major forms of melanin?

Answer 5

• pheomelanin is yellowish-reddish
• eumelanin is black-brown

Question 6

How is melanin distributed?

Answer 6

different proportions in the skin and hair

• light skin mostly produce pheomelanin
• dark skin mostly produce eumelanin

Question 7

Why is there different skin colour?

Answer 7

skin colour is an adaptation to UVR exposure

Question 8

How is skin colour an adaptation to UVR exposure?

Answer 8

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

Question 9

What is the geographic distribution of skin colour?

Answer 9

Question 10

How does light vs. dark skin protect for skin cancer?

Answer 10

• 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

Question 11

death from melanoma and other skin cancers

Answer 11

Question 12

what is a natural sunscreen?

Answer 12

melanin

Question 13

What is folate?

Answer 13

a B vitamin

• froms RBCs and DNA synthesis, and developed the fetus nervous system

Question 14

Whats food contain folate?

Answer 14

food sources include

• raw green leafy vegetables
• citrus fruits
• organ meats
• breads, cereals and pasta have fortified white flour with folate

Question 15

What destroys folate and what protects it?

Answer 15

UV rays destroys folate but skin pigmentation can protect from it

• dark skin protects against the photodegradation of folate in the skins blood vessels

Question 16

What does Vitamin D do?

Answer 16

vitamin D regulates intestinal Ca absorption, enables bone mineralization, and is needed for bone formation and remodeling

Question 17

What does Vitamin D deficiency lead to?

Answer 17

• 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

Question 18

what is rickets?

Answer 18

Bowed legs usually occuring in children because legs cannot support weight of child due to poor mineral absorbtion

Question 19

What is osteomalacia, osteopinia and osteoporisis?

Answer 19

• osteomalacia: bones demineralizer and soften
• osteopinia: bone thinning
• osteoporosis: brittle bones

Question 20

Natural foods containing Vitamin D₃ and D₂

Answer 20

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}

Question 21

Who is at risk of vitamin D deficiency in terms of diet?

Question 22

How is Vitamin D₃ synthesized?

Answer 22

D₃ is synthesized in the skin by the reaction of 7-dehydrocholesterol with solar UVB radiation

Question 23

How does cutaneous production of Vitamin D₃ change?

Answer 23

• 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)

Question 24

What skin pigment facilitates Vitamin D production?

Answer 24

• 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

Question 25

What extrinsic factors effect Vitamin D synthesis?

Answer 25

• modest clothing in many cultures preventing exposure of skin for D synthesis. both in warm and cold places
• air quality - smog limits amount of sunshine received
• sunscreen filters out UVB
• cultural values about skin lightness