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Vitamin D: The Hottest Nutrient Under the Sun

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Vitamin D: The Hottest Nutrient Under the Sun

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    1. Vitamin D: The Hottest Nutrient Under the Sun Keli M. Hawthorne, MS, RD, LD Baylor College of Medicine Childrens Nutrition Research Center Texas Childrens Hospital kelih@bcm.edu

    2. History of Vitamin D Identified in 1919 but improperly named as a vitamin Actually a prohormone Structurally similar to steroid hormones (ie, cortisol, estradiol, and aldeosterone) 2 main forms: D2 (ergocalciferol) and D3 (cholecalciferol)

    3. Whether from skin or dietary sources, vit D accumulates in the liver where it is hydroxylated to 25OHD and then enters circulation. The conversion to 1,25OHD occurs in the kidneys and this process is tightly regulated by PTH in response to serum Ca and Phos levels. Whether from skin or dietary sources, vit D accumulates in the liver where it is hydroxylated to 25OHD and then enters circulation. The conversion to 1,25OHD occurs in the kidneys and this process is tightly regulated by PTH in response to serum Ca and Phos levels.

    4. Functions of Vitamin D To aid in the intestinal absorption of calcium and phosphorus, thereby promoting strong bones Role in cellular metabolism Antiproliferation, prodifferentiation

    5. Effects of Deficiency Rickets (children) Osteomalacia (adults) Elevated serum PTH Decreased serum phosphorus Elevated serum alkaline phosphatase Osteoporosis Epidemiological evidence of increased risk of colon, breast, and prostate cancer

    6. Measurement 1,25(OH)D active metabolite of vitamin D, but a poor marker for vitamin D status because it doesnt indicate body stores 25-hydroxyvitamin D 25(OH)D3 Inactive metabolite but a better indicator of vitamin D status Should be analyzed with RIA

    7. PTH:Vitamin D interaction Inverse relationship between 25(OH)D levels and PTH Increased fractional absorption of calcium is associated with increased PTH levels, not 25(OH) D levels Consequences of low 25(OH) D levels are not obvious. Compensation with increased PTH and production of 1,25 (OH) D with resultant normal calcium absorption appears appropriate 1,25 (OH) D levels are pending in this cohort However, this sequence may be inadequate under stress situations such as low mobility, very low dietary calcium, chronic illnesses

    8. Factors that Affect Production of Vit D from UV-B Radiation Time spent outdoors Time of day Latitude, altitude Season Air pollution Degree of clothing Skin pigmentation Age Cloud cover Ozone column Sunscreen

    9. Let the Sun Shine Affect of Sunscreen: SPF 8 decreases vitamin D production by 95% No known cases of Vit D toxicity with extreme or prolonged sun exposure Chronic sun exposure among outdoor workers at the end of summer equate to 25(OH)D levels similar to 2800-5000 IU/d supplementation Barger-Lux & Heaney. J Clin Endocrinol Metab 2002

    10. Special Populations Dark skin pigmentation Elderly Infants Obese Limited Sunlight Exposure

    11. Individuals with Dark Pigmentation of Skin High melanin content in the skin reduces the skins ability to produce vit D from sunlight Higher risk of deficiency who may benefit even more from a supplement (especially older women)

    12. Based on data from NHANES 3, AA adults consumed fewer calcium supplements, less milk and less cereal than white adults, resulting in lower total vitamin D intakes. This combined with increased skin melanin results in significantly lower 25(OH)D levels with AA adults in the deficient range in this study. Based on data from NHANES 3, AA adults consumed fewer calcium supplements, less milk and less cereal than white adults, resulting in lower total vitamin D intakes. This combined with increased skin melanin results in significantly lower 25(OH)D levels with AA adults in the deficient range in this study.

    13. Even when intakes are accounted for in the calculations, AA adults still had lower 25(OH)D levels than white adults.Even when intakes are accounted for in the calculations, AA adults still had lower 25(OH)D levels than white adults.

    14. Elderly Vit D deficiency leads to: Muscle weakness Loss of balance Decreased lower extremity function And therefore, more FALLS and HIP FRACTURES At what 25(OH)D level? Generally, >74 nmol/L in Caucasians Higher in older adults of darker skin color Another high risk group: Elderly As people age, skin cannot synthesize vit D as efficiently and the kidneys are less able to convert vit D to its active hormone form. Its estimated that 30-40% of older adults with hip fractures are vit D insufficient.Another high risk group: Elderly As people age, skin cannot synthesize vit D as efficiently and the kidneys are less able to convert vit D to its active hormone form. Its estimated that 30-40% of older adults with hip fractures are vit D insufficient.

    15. Changing What We Know In 1997, the recommended intake for elderly adults was _____. Currently its ______.In 1997, the recommended intake for elderly adults was _____. Currently its ______.

    16. Breastfed Infants Breast milk provides ~25 IU vit D/L DRI recommends 200 IU/d for breastfed infants who are not exposed to sunlight (ie, northern latitudes) AAP recommends 200 IU/d for all breastfed infants (with no geographical or racial distinctions) beginning in the first 2 months of life unless weaned to at least 500 mL infant formula Plenty of Vit D in infant formulas to avoid ricketsPlenty of Vit D in infant formulas to avoid rickets

    17. Questionable Benefits in Pregnancy Low maternal 25(OH)D levels may result in decreased whole body BMC (r=0.21, p=0.009) and spine BMC (r=0.17, p=0.03) when the child is 9 yrs old Javaid et al, Lancet Jan 2006 Compared to pregnant women with 25(OH)D levels <30 nmol/L, women with 25(OH)D levels >75 nmol/L were not associated with childs body size, intelligence, psychological health, or cardiovascular system; possible increased risk of eczema at 9 mo of age (OR 3.26, 95% CI 1.15-9.29, p<0.03) and asthma at 9 yrs of age (OR 5.4, 95% CI 1.09-26.65, p<0.04) Gale et al, Eur J Clin Nutr 2008

    18. Obese Vit D is stored in bodys fat cells and is unavailable for use Even if adequate Vit D is produced in the sun, it may not be physiologically available No data on recommended amounts to increase based on body weight range

    19. Limited Sunlight Exposure Homebound individuals Living in northern latitudes Wearing robes & head coverings for religious reasons Working in occupations that prevent sun exposure Need to be more cognizant of dietary intake or consider supplementation

    20. As latitude increases to the north, vitamin D activation through sunlight decreases. 37 degrees latitude appears to be an important cutoff for vitamin D activation.As latitude increases to the north, vitamin D activation through sunlight decreases. 37 degrees latitude appears to be an important cutoff for vitamin D activation.

    21. 37o Latitude Cutoff for Vit D

    22. Vitamin D, PTH and Bone Mass in Late Adolescence in Finland

    23. Vitamin D Levels in Adolescents in Boston

    24. Vitamin D Deficiency (= 37 nmol/L) in Boston Adolescents About half of the AA teens in Boston were vit D deficient along almost 1 in 5 Hispanic teens. About half of the AA teens in Boston were vit D deficient along almost 1 in 5 Hispanic teens.

    25. Vitamin D and PTH in Adolescents in Boston As vit D levels improve, PTH decreases. What cutoff - 37?As vit D levels improve, PTH decreases. What cutoff - 37?

    26. Houston, We Have a Problem

    27. 25-(OH)D Levels by Ethnicity

    28. Low Vitamin D Levels (= 50 nmol/L) in Houston White = 3/44 = 9% African-American = 8/15 = 53% Hispanic = 2/20 = 10% Asian = 2/10 = 20% Overall, 17% with low levels. Ethnic groups different, p < 0.01. Question is, what does this mean functionally?

    29. Suboptimal Vitamin D levels (= 80 nmol/L) in Houston White = 27/44 = 61% African-American = 14/15 = 93% Hispanic = 15/20 = 75% Asian = 9/10 = 90% Overall, 65/89 = 73% suboptimal

    30. Vitamin D Status of Young Adolescents Recent data from US and elsewhere indicate possible vitamin D deficiency among adolescents New dietary recommendations (US) suggest that a level of up to 80 nmol/L for 25(OH)D might be optimal Physiological consequences of low vitamin D levels are not clear for adolescents.

    31. Vitamin D and PTH in Adolescents in Houston

    32. Recommendations

    33. Current Recommendations

    34. Affect of Supplementation For each additional 100 IU/d of D3, serum 25(OH)D increases by 1-2 nmol/L Fair evidence that 800 IU/d Vit D3 and 1200 mg/d calcium can decrease fracture risk in older individuals

    36. Improvements in 25(OH)D with Supplementation How much vitamin D suppl?How much vitamin D suppl?

    37. Are the Current AIs Enough? Consensus is NO Historically, normal level of Vit D was 30 nmol/L; now considered deficient At least 50 nmol/L necessary for proper function 78-100 nmol/L for bone health, fracture prevention, and chronic disease prevention Holick MF. AJCN 2004 Bischoff-Ferrari et al. AJCN 2006

    38. Changing What We Know 1997: 30 nmol/L is sufficient Present: 80 nmol/L is sufficient

    39. What should the UL be? Current UL is 2,000 IU/d Most agree this is far too low Discourages food & beverage companies from fortifying with higher levels of Vit D Level to avoid toxicity symptoms First symptom appears as hypercalcemia Seen with 25(OH)D at 500 nmol/L (but usually 650-700 nmol/L)

    40. Changing What We Know Current NOAEL: 60 mcg/d Recommended NOAEL: 265 mcg/d

    41. What should the UL be? Report to IOM Food and Nutrition Board Reviewed over 20 trials with supplementation ranging from 2144-100,000 IU/d Concluded that 10,000 IU/d Vit D is safe At this level, 25(OH)D concentrations remain well below 500 nmol/L Add referenceAdd reference

    42. Sources of Vitamin D Few natural food sources Fatty fish (salmon and tuna), cod liver oil Fortified foods make up 65-87% in US diet Milk, cereals, orange juice Dietary Supplements Adequate sunlight exposure Duration of exposure is variable based on skin pigmentation and latitude Fortified foods make up 65-87% in US diet (according to NHANES 1999-2000)Fortified foods make up 65-87% in US diet (according to NHANES 1999-2000)

    43. Vitamin D Intakes

    44. Sources of Vitamin D

    46. Vitamin D Levels Based on Fortified Juice for 1 Year

    47. Change in Vitamin D Levels After 1 Year

    48. Whats on the Food Label? Not Vitamin D! Lack of Vit D content info on Nutrition Facts Food Label is a critical barrier to improving Vit D intakes of natural food sources

    49. Vitamin D and Disease

    50. Low Vitamin D Status is also associated with Reduced lower extremity neuromuscular function Increased risk of Type I Diabetes Impaired insulin sensitivity Increased risk of metabolic syndrome Increased risk of Multiple Sclerosis With 25(OHD) > 100 nmol/L, 62% reduction in risk for MS compared to patients with 25(OH)D < 63 nmol/L Impaired immune response Increased risk of influenza and respiratory infections Increased risk and severity of tuberculosis Increased risk of various cancers Breast, colon, lung, prostate, marrow, lymphoma

    51. Vitamin D and Cancer Incidence Inverse relationship found for 25(OH)D levels and risk for all types of non-skin cancers With 25(OH)D > 80 nmol/L, there was a 50% reduction in colorectal cancer risk With 25(OH)D > 50 nmol/L, there was a 50% reduction in prostate cancer risk Lappe et al, AJCN 2007 Tuohimaa et al, Int J Cancer 2004

    53. How much vitamin D does the body need to produce a serum level that protects against disease?

    54. Reaching Optimal 25(OH)D Levels

    55. Summary Be aware that recommendations for intakes and the UL will likely change soon Groups at higher risk for vitamin D deficiency should emphasize fortified and natural food sources in addition to supplementation 25(OH)D levels: Deficient: <50 nmol/L Sufficient: 50-80 nmol/L Vitamin D intakes: Current UL is 2000 IU/d although new data show that 10,000 IU/d is safe

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