Case 5: Skin, Vitamin D, Folate, Melanoma

Oral intake of Vitamin D

*1-70 years of age:* 600 IU/day (15 μg/day) *Pregnant/lactating:* 600 IU/day (15 μg/day) *71+ years of age:* 800 IU/day (20 μg/day) Some nutritionalists are recommending 1,000-2,000 IU/day

Case 5c: Which evolutionary pathway(s) is/are demonstrated in this case?

*An evolutionary mismatched or novel environment:* - This woman's ancestral population evolved to have modest exposure to sun which was adequate for proper vitamin D production. - Due to her behavioral mismatch of lying inthe direct sun for long periods of time most days, this woman has a lifetime of much higher exposure to sun than her ancestral populations, even though she lives at a similar latitude as her ancestral populations. *Outcome of cultural choice:* - To frequently lay in the sun:

Calcitriol to Vitamin D

*Calcitriol binds to vitamin D-binding protein*, a carrier protein in the plasma, that *transports calcitriol to various target organs.*

Cholecalciferol to calcidiol

*Cholecalciferol synthesized in the skin* is carried in bloodstream to the liver, where it is *converted into prohormone calcidiol* (25-hydroxycholecalciferol = 25-hydroxyvitamin D3)

Calcidiol to calcitriol

*Circulating calcidiol is then converted in the kidneys into calcitriol* (1,25- dihydroxycholecalciferol = 1,25- dihydroxyvitamin D3), the biologically active form of vitamin D which functions as a hormone.

Epidermis cell types

*Keratinocytes:* most common cell type in epidermis and are full of keratin *Melanocytes:* located in basal layer; manufacture and secrete pigment *Tactile epithelial cells:* located in basal layer; attached to sensory nerve endings *Dendritic cells:* located in stratum spinosum; part of immune system; macrophage-like

Melanocytes & Melanoma

*Melanocytes:*Cells that produce the dark pigment, melanin, which is responsible for the color of skin. *Melanoma* A malignant tumor of melanocytes. - Particularly common among light skinned humans - High rates of incidence in Australia, New Zealand, North America, and parts of Europe.

Case 5b: Which evolutionary pathway(s) is/are demonstrated in this case?

*Outcomes of demographic history:* - Boy's ancestral lineage evolved in equatorial area of Africa with high sun and UV exposure and evolved high levels of melanin to protect skin. - This infant was born and lives in a USA city at a much higher latitude with less sun and UVB exposure compared to his ancestral lineage from Africa. *An evolutionary mismatched or novel environment:* - Boy's ancestral lineage evolved in equatorial area of Africa with high sun and UV exposure and evolved high levels of melanin to protect skin. - Ancestral lineage population requires up to 10 times the sun exposure compared to lighter skinned people to make adequate levels of vitamin D. - This infant was born and lives in a USA city at a much higher latitude with less sun and UVB exposure compared to his ancestral lineage from Africa. - This boy is seldom taken outside. - This has resulted in a very diminished exposure to UVB for vitamin D production compared to what his ancestral lineage was used to. - This boy has been exclusively breast fed with no cows milk, formula, or vitamin supplements. - The ancestral populations in West Africa also exclusively breast fed, however, infants and children were exposed to generous amounts of direct sunlight and UVB which was the source of the vitamin D. - The child in case 2b had a dramatic mismatch in level of sun exposure for vitamin D production compared to his ancestral population in Ghana.

Case 5d: Which evolutionary pathway(s) is/are demonstrated in this case?

*Outcomes of demographic history:* - This woman's ancestral population from northern Europe evolved to have low levels of melanin so they could manufacture adequate skin vitamin D with limited sun exposure. - Because the ancestral environment had such limited annual sun exposure, even with the low melanin, little of the folate was broken down by the UV light and hence serum levels were maintained in normal range. - Since this women lives in an area with much greater UVB exposure than her ancestral environment, her serum folate levels are being depleted. *An evolutionary mismatched or novel environment:* - This woman's ancestral population evolved to have modest exposure to sun which was adequate for proper vitamin D production without destroying significant amounts of serum folate. - The geographical location where this woman lives and her behavior of being outdoors much of the time, created an evolutionarily mismatched environment that has caused her to have a much higher exposure to UV than her ancestral populations. - While this increased sun exposure has increased her vitamin D levels, it has depleted her folate levels. - This woman's ancestral population evolved to eat leafy greens such as kale and cabbage which are good sources of folic acid. - The high meat and dairy and low vegetable and fruit diet resulted in a low folic acid intake which contributed to her low serum levels of folate. - This has contributed to her low serum folate levels.

Female melanin levels

- *Maternal melanin levels drop during pregnancy* so she can *more efficiently manufacture vitamin D on her skin to aid in calcium absorption* - Maternal calcium needs increase during pregnancy and lactation because the mother must provide enough calcium for fetal and neonatal skeleton development. - Infants also have lower levels of melanin than older children and adults which enables them to produce more vitamin D in their skin. - A trade off is that the lighter skin results in more depletion of folate in blood. - *Females have lighter skin than males (lower melanin than males)*, most likely *to facilitate greater vitamin D3 production to aid in calcium absorption for proper bone deposition*

Skin melanin, vitamin D and folic acid

- *Melanin* in skin is *inversely related to vitamin D production* - *Melanin* in skin is *inversely related to folic acid destruction in blood* - High melanin levels is related to high folic acid blood levels and low vitamin D production from UVB. - Low melanin levels is related to low folic acid blood levels and high vitamin D production from UVB.

Folate deficiency

- A serum folate of *3 μg/L or lower* indicates deficiency. - An erythrocyte folate level of *140 μg/L or lower* indicates inadequate folate status. - Treated with supplemental oral folate of 400 to 1000 μg per day or diet rich in folate. Results in: - Macrocytic anemia - Impairment of DNA synthesis and repair - Peripheral neuropathy - Neural tube defects (e.g., spina bifida and anencephaly) in developing embryos - Increased risk for cleft lip and palate

Folic acid for pregnant and lactating women

- All pregnant women are recommended to take a daily oral supplement of folic acid prior to conception and throughout their pregnancy and lactation. - Women who get 400 micrograms (0.4 milligrams) daily prior to conception and during early pregnancy reduce the risk by 70% that their baby will be born with a serious neural tube defect (a birth defect involving incomplete development of the brain and spinal cord)

Light skin covered by dark hair

- Based on an examination of the variation in MC1R nucleotide sequences, it is estimated that roughly *five million years ago*, after the evolutionary separation of chimpanzees and humans, the common ancestors of humans had light skin that was covered by dark hair. - Today, our closest extant relative, the chimpanzee, continues to have light skin covered by dense body hair.

Causes of poor Vitamin D levels in 5b child

- Breast milk is a poor source of vitamin D for infants. - This child does not spend very much time outdoors. - Michigan is quite cold six months out of the year and the winter daylight hours are short. - Amount of UV radiation is significantly lower in Michigan, compared to Ghana.

Vitamin D (cholecalciferol) production

- Cholecalciferol is produced in the deep epidermis in the stratum spinosum and stratum basale. - The melanin in the keratinocytes blocks the penetration of UV into the epidermis and shields the cell nuclei from incoming UV radiation. - Inverse relationship between level of melanin in skin and ability of skin to manufacture vitamin D at a given UV exposure.

Melanin and UV radiation

- Darker skinned people have darker melanin and more pigment in each melanocyte. - In all but the darkest skinned people, melanocytes respond to ultraviolet radiation by increasing production of melanin and increasing its transfer to keratinocytes, the protective response which results in a suntan. 26

Ancestral sources of vitamin D

- Given the fact that breast milk does not contain adequate levels of vitamin D, humans have evolved to consistently get vitamin D from the SUN. - Throughout evolution, humans have spent a lot of time outside exposed to the sun, often without clothing. - Humans of all ethnicities have the least amount of melanin when they are newborns and infants; this enables infants to increase the use of sunlight UVB to synthesize vitamin D. - Also, women have a reduction in their levels of melanin during pregnancy which enables them to more efficiently manufacture vitamin D from sun exposure; a woman's vitamin D requirement increases when she is pregnant.

Too little sun exposure, vitamin D deficiency and environmental & behavioral mismatches

- Humans from latitudes from all over the world evolved to have modest direct exposure of sun on their skin. Males and females with low levels of vitamin D can: - Develop *rickets (children)* or *adult osteomalacia* - Higher rates of *autoimmune disease* - Higher rates of *autism* - Higher rates of *hypertension* Men with low levels of Vitamin D can have higher rates of *prostate cancer* Women with low levels of Vitamin D can have: - Higher rates of *breast cancer* - Higher rates of *bacterial vaginosis* - Higher rates of *C-section*

Melanin level as outcome of demographic history

- Humans with highest levels of melanin tend to have ancestors who originated from regions of the world (e.g., equatorial latitudes) where they have been exposed to large amounts of UV light. - Humans with low levels of melanin tend to have ancestors who originated from regions of world north of the equator exposed to lower levels of UV light.

Low Vitamin D levels cause increased risk for:

- Hypertension - Breast cancer - Prostate cancer - Inflammatory disease - Several autoimmune diseases - Cesarean section

Vitamin D functions

- Maintain normal blood levels of calcium and phosphorus. - Aids in absorption of calcium by the intestine. - Promotes healthy mineralization, growth and remodeling of bone which helps to form and maintain strong bones. - Prevents hypocalcemic tetany.

Layers of Epidermis: Stratum basale

- Melanocytes—spider shaped melanocytes make up 10-25% of the cells in stratum basale - Melanocytes make melanin and transport it through its spider shaped cells process to nearby keratinocytes

Natural selection of melanin level

- Natural selection favors high pigmentation in areas of high sun and high ultraviolet exposure to protect against ultra-violet light skin damage and skin cancer. - Natural selection favors decreased pigmentation in areas of low sunlight and ultraviolet exposure to increase vitamin D synthesis.

Folate deficiency effect on pattern forming genes

- Neural tubes close in the early weeks post conception. - Folate deficiency in embryos before neural tube closure increases the likelihood of neural tube defects e.g., spina bifida and anencephaly. - It appears that this nutritional deficiency in the embryo may affect the expression or action of pattern-forming genes. - Folic acid supplement is recommended for all pregnant women.

Vitamin D levels inversely related to bone fractures in girls

- Over 9,000 girls 9 to 15 years of age were followed over a 7 year period. - 4% of these girls developed a bone stress fracture and 90% of these girls participated in at least an hour a day of high-impact physical activity - Girls in the group with the 20% highest intake of vitamin D were 52% less likely to develop a fracture than girls in the group with the 20% lowest intake of vitamin D.

To little sun exposure and vitamin D deficiency

- People of all skin color types who consistently use sunscreen, wear concealing clothing, and/or stay inside much of the day are at increased risk for vitamin D deficiency - There is an epidemic of vitamin D deficiency in the USA among all ethnicities - A recent study in the USA on levels of Vitamin D deficiency shows that African- Americans have prevalence rates of 52-76%, 18-50% in Latinos, and 8-31% in European- Americans

Vitamin D production & skin melanin

- People with dark skin require up to 10 times more exposure to sunlight than people with light skin to produce the same amount of Vitamin D. - Darker skinned people who live in more northern latitudes than is represented in their evolutionary history, are at risk for Vitamin D deficiency. - A recent study in the USA on levels of Vitamin D deficiency shows that African- Americans have prevalence rates of 52- 76%, 18-50% in Latinos, and 8-31% in European-Americans.

Vitamin D and skin color

- People with dark skin require up to 10 times more exposure to sunlight than people with light skin to produce the same amount of vitamin D. - Darker skinned people who live in more northern latitudes than their ancestors, are at risk for vitamin D deficiency. - Lighter skinned people who live in equatorial areas are at increased risk for skin cancer

Benefits of pigmentation

- Pigmentation (melanin) serves to regulate the effects of UV radiation in the contents of cutaneous blood vessels located in the dermis. - High skin melanin levels contribute to darker skin color which protects against sunburn, skin cancer, and the destruction of nutrients (e.g., folic acid) in the skin.

Selective forces on pigmentation

- Pigmentation decreases when vitamin D3 production needs are increased. - Pigmentation increases to protect against UV damage to folate in blood as well as skin cell nuclei. - Both vitamin D and folate are necessary for reproductive success so for good health there should be a balance between the requirements for these two nutrients.

Folate deficiency during pregnancy increases risk of

- Preterm delivery - Infant low birth weight - Fetal growth retardation - Increased homocysteine level in the blood, which may lead to spontaneous abortion and pregnancy complications

Melanin in skin

- Sensitivity of skin to UV radiation is influenced by its level of melanin. - Most people with light skin can increase their level of melanin by moderate exposure to sun over days or weeks which stimulates increased output of melanocytes (suntan) that is an example of physiological plasticity. - Long term exposure to different amounts of sunlight at different latitudes has created a spectrum of human skin colors influenced by the variation in the amount and type of melanin in the skin, with an almost linear relationship between latitude of population origin and skin melanin levels - It is believed by many evolutionary biologists that the selective pressure for lighter skin color in northern latitudes arose from the need to maximize vitamin D production in the skin in areas of relatively low ultraviolet B availability.

Sources of vitamin D3 (cholecalciferol)

- Sun exposure on skin - Fish - Eggs - Liver - UV-irradiated mushrooms and yeast are the only known significant vegan food sources of vitamin D3

Behavioral factors that reduce Vitamin D production in the skin

- Sunscreen - Concealing clothing - Spending much of the day inside - Excessive use of soap on areas of skin exposed to sun - Choice to live in an area with low number of sunny days out of each year

Vitamin D2 (ergocalciferol)

- Synthesized by plants and can be obtained by eating these plants - Much less potent form of vitamin D compared to vitamin D3 - Much less effective at elevating blood 25- hydroxyvitamin D levels - Shorter shelf life than vitamin D3 - Vitamin D3 is recommended over vitamin D2 as a human supplement to maintain normal blood 25-hydroxyvitamin D levels

Genetic Evidence for Convergent Evolution of Light Skin in Europeans and East Asians through different SNP mutations

- The SNP (single nucleotide polymorphism) genetic mutations leading to light skin, are different among East Asians and Europeans. - The two groups likely experienced a similar selective pressure due to settlement in northern latitudes.

Increase in epidermal permeability barrier

- The skin tone grew darker to increase the epidermal permeability barrier. - Essential protective functions of the skin, including the permeability barrier and the antimicrobial barrier, reside in the stratum corneum. - The loss of body hair likely triggered an increase in genetic change related to the stratum corneum as natural selection favored mutations that protect this essential barrier.

Folate

- This important vitamin undergoes photolysis when exposed to UV light, which can contribute to a folate deficiency. - Increased skin pigmentation protects the folate from photolysis in the presence of UV light. - Folate deficiency is less prevalent among people of African descent. - Folate deficiency and neural tube defects are more prevalent among people with less skin pigmentation. - There is an increased incidence of neural tube defects with maternal tanning bed use, which exposes the skin to direct UV light resulting in folate photolysis.

Case 5b: Bowed legs in a 2 y/o male

A 2 year old African American breast fed male from Detroit, Michigan presents with bowed legs. This boys ancestors are from the Ashanti tribe in the West African country of Ghana. This child has been exclusively breast fed and has had no cows milk, formula, or vitamin D supplements, but does eat a spectrum of ground up vegetables, fruits, and meat. Mom reports that she does not take him out in the direct sun very often. *Lab results:* Decreased plasma calcium, phosphorus, and vitamin D *Rickets:* Causes softening of bones in children which can potentially lead to bone deformity (e.g., leg bowing) and fractures. - Predominant cause is vitamin D deficiency. - Can also be caused by low calcium intake.

Calcium

Normal vitamin D levels are essential for proper absorption of dietary calcium

Effects of low vitamin D levels

Thin, brittle, and weak bones *Rickets:* osteomalacia in children *Osteomalacia in adults:* softening of bones due to defective bone mineralization which can lead to bone malformation and lower back pain and thigh pain *Osteoporosis in adults:* reduction on bone density especially in women

Vitamin D3 (cholecalciferol)

*Synthesized from 7-dehydrocholesterol in the deep epidermis (stratum basale & stratum spinosum)* of human skin when exposed to ultraviolet-B (UVB) rays from the sunlight.

Vitamin D in infants

- Adequate Vitamin D is required for growth and development of infants - Breast milk is a poor source of vitamin D - Human infants have evolved spending enough time outside to provide them with regular skin exposure to sunlight to produce vitamin D. - Compared to adults, newborns and infants have lower levels of melanin to maximize their ability to utilize sunlight for vitamin D production.

Dietary sources of calcium

- Beans, including soy products - Nuts and seeds - Whole grains - Leafy greens, broccoli - Dairy products

Too much sun exposure and environmental & behavioral mismatches

- Humans from latitudes from all over the world evolved to have modest direct exposure of sun on their skin. - Adequate Vitamin D production is essential for proper bone development. - However, too much sun exposure (and tanning salon exposure) especially in lighter skinned people increases their risk for skin cancer; this is an example of an environmental mismatch and a behavioral mismatch.

Serum 25-hydroxyvitamin D3

- Levels of 30 to 50 ng/ml are now considered to be in the desirable range by many dieticians and physicians. - Some consider 40 to 80 (or even 100) ng/ml to be the desirable range

Spina bifida

- Spina bifida in fetus and newborn is associated with pregnant mothers who have low levels of serum folate. - This woman's serum folate was checked and found to be well below normal levels.

Case 5d:

30 y/o fair-skinned northernEuropean-American female primagravida who had no prenatal care presents to the hospital and delivers a 8 pound baby girl with spina bifida. Mom has no prior history of health problems. *Dietary history:* eats mainly meat and dairy products and not very many vegetables and fruits and no vitamin supplements. *Behavioral history:* lived most of her life in southern Florida where she has spent a fair amount of time doing outdoor activities and reports only occasionally using sunscreen.

Vitamin D

Fat soluble secosteroid

Skin pigmentation effect on vitamin D3 and folate

Low pigmentation Increased UV light exposure Increased *vitamin D production* Increased *folate depletion* in blood

B9 (folic acid and folate): Essential to numerous bodily functions such as

Water soluble vitamin - Synthesis, repair, and methylation of DNA. - Cofactor in numerous biological functions. - Development of neural tubes in embryos. • Aids rapid cell division and growth in fetuses and infants. - Bone marrow maturation. - Red blood cell production.

Case 5a: Which evolutionary pathway(s) is/are demonstrated in this case?

*Outcome of demographic history:* Her ancestors were apparently not cow herders and did not retain lactase into adulthood, hence she is lactose intolerant and is not able to drink Vitamin D enriched cows milk. *Life-history associated factors:* This adult is at developmental stage in which she is not able to digest lactose which has resulted in her not drinking vitamin D enriched cows milk. *An evolutionary mismatched or novel environment:* Woman's ancestral lineage evolved to have modest exposure to sun for vitamin D production; this woman consistently avoids sun exposure by wearing concealing clothing and sunscreen and staying indoors much of the time. *Outcome of cultural history:* Woman has voluntarily chosen to consistently avoid sun exposure by wearing concealing clothing and sunscreen and staying indoors much of the time.

Vitamin D2 and D3

*Vitamin D2 (ergocalciferol):* obtained from plant foods *Vitamin D3 (cholecalciferol):* from sunlight on skin and from some animal foods and some fungi

Human migration and skin color

- *100,000 to 70,000 YA*, as populations began to migrate, the level of skin melanin typically decreased proportionally to the distance North a population migrated, resulting in a range of skin tones from the equator up to more northern latitudes. - Under conditions of less UV light exposure in northern latitudes, there was less photodestruction of folate. - In addition, lighter skin is able to generate more vitamin D (cholecalciferol) than darker skin given the same UV light exposure, resulting in a health benefit and selective advantage in reduced sunlight.

Vitamin D synthesis

- *Cholecalciferol* formed in skin from 7- dehydrocholesterol - *Calcidiol* (25-hydroxyvitamin D3) formed in liver - *Calcitriol* (1,25-dihydroxyvitamin D3) formed in kidney, which is the biologically active form of vitamin D which functions as a hormone. - Vitamin D-binding protein binds to calcitriol and transports it in plasma to other organs

B9 (folic acid and folate)

- Folate and folic acid derive their names from the Latin word folium (which means "leaf"). - Important sources of folate are leafy green vegetables (e.g., kale & spinach) & some fruits e.g. oranges. - Folate consumed in the diet is metabolized in the liver to produce bioactive metabolites. - The terms folic acid and folate are often used interchangeably for the water-soluble B9 vitamin. - Folic acid occurs rarely in foods or the human body but is the form most often used in vitamin supplements and fortified foods and is easily bioavailable. - Naturally occurring folates exist in many chemical forms. - Folates are found in plant foods as well as in metabolically active forms in the human body. - People who regularly consume folate will have 500 - 20,000 μg of folate in body stores. - With complete lack of dietary folate intake, it can take months before these stores are depleted.

*Too much* sun exposure and environmental & behavioral mismatches

- Humans from latitudes from all over the world evolved to have modest direct exposure of sun on their skin. - Adequate vitamin D production is essential for proper bone development. - However, too much sun exposure (and tanning salon exposure) especially in lighter skinned people increases their risk for skin cancer. - This is an example of an environmental mismatch and a behavioral mismatch.

*Modest* sun exposure & environmental and behavioral matches

- Humans from latitudes from all over the world evolved to have modest direct exposure of sun on their skin. - Adequate vitamin D production is essential for proper bone development. - People with moderate tans have higher vitamin D levels and lower rates of breast cancer and prostate cancer. - A balance (match between evolutionary history, and contemporary environment and behavior) between enough sun and not to-much sun exposure is important. This balance is a match between evolutionary history and contemporary environment and behavior.

Hair loss

- It is suggested that over time human hair disappeared to allow better heat dissipation through sweating. - However, other evolutionary biologists believe that hair loss was triggered by sexual selection.

Case 5c: Enlarging dark mole (nevus) on skin of forearm of 28 year old female

28 year old European-American female with ancestors from northern Italy presents with enlarging dark brown lesion on skin of forearm. No prior history of skin problems or other health problems. Behavioral history: Lived most of her life in southern Florida where she spent a lot of her free time laying on beaches and used very little sunscreen. Melanoma lesions are asymmetrical, have irregular borders, and variable color.

Case 5a: Lower back and thigh pain in 35 y/o European-American female

35 y/o European-American female from Seattle comes into the clinic with lower back pain and thigh pain. Reports that she has had pain for several months that is getting worse, with no history of injury to back or thighs. Dietary history: diverse omnivorous diet but does not consume dairy products because she has lactose intolerance. She does not take a vitamin D supplement. She always wears protective, covered clothing and does not go out much everyday. *X-ray findings:* Pseudofractures of proximal femurs with decreased density inside surface of bone with thickened periosteum is indicative of osteomalacia-- the softening of the bones caused by decreased bone mineralization caused by vitamin D deficiency, diminished sun exposure to skin, and lack of vitamin D in diet. *Lab results:* Decreased plasma calcium, plasma phosphorus, vitamin D.

Pigmentation

An adaptation to the presence of UV light that contributes to fitness by influencing vitamin D3 and folate levels in the body.

Genetic Variation at the MC1R Locus and the Time since Loss of Human Body Hair

Around *1.2 million years ago* it is estimated that the skin of Homo erectus was dark and mainly hairless and this continued in Homo for the next 1.1 million years *until 100,000 years ago* when the first Homo sapiens started migrating out of Africa.

Clines

Continuous geographical gradient of a trait - With many human characteristics/traits there is a continuous geographical gradient of a trait rather than discontinuous variation. - Because of the north-south clines that exist for skin melanin, there is often a gradual and progressive change along a clinal gradient rather than discontinuous variation. - Hence, the designation of race based on skin melanin is erroneous...there are no races, but only clines which demonstrate a continuous spectrum of variation within Homo sapiens - Genetic analysis of alleles undergoing clinal traits demonstrates corresponding clinal variation in allele frequencies. - Our genotype, and consequently our phenotype, are determined by the position of our indigenous origin on a multitude of intersecting clines. - The continuous variation in human traits on gradients which vary in orientation means that there are no boundaries, geographical or genetic, which can be used to assign individuals to particular races....there are no races, only clines. - Similarly, intrapopulation and interpopulation variation in disease risk tends to be clinal and not racial. - Clinal variation can also be demonstrated within and between ethnolinguistic groups.

Maintenance of normal folate levels is associated with

Increased fitness

Human skin pigmentation as an adaptation to UV radiation

Skin pigmentation reduces folate depletion by reducing the exposure to UV from sunlight.

Layers of Epidermis

Stratum corneum (outer layer) Stratum lucidum (only in thick skin) Stratum granulosum Stratum spinosum Stratum basale (most inner layer)

Influence of developmental experience and evolutionary history on susceptibility to sunburn

Susceptibility to sunburn is influenced by ancestral evolutionary origin (skin color) and past sun exposure (suntan).