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Dose Response to Vitamin D Supplementation in Postmenopausal Women

Dose Response to Vitamin D Supplementation in Postmenopausal Women. Annals of Internal Med. 2012; 156:425-437. Jayme Bristow.

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Dose Response to Vitamin D Supplementation in Postmenopausal Women

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  1. Dose Response to Vitamin D Supplementation in Postmenopausal Women Annals of Internal Med. 2012; 156:425-437 Jayme Bristow

  2. To determine the effect of increasing oral doses of Vitamin D3 on serum 25-[OH]D and serum parathryoid hormone (PTH) levels in postmenopausal white women with Vitamin D sufficiency with sufficient calcium intake Objectives

  3. The Institute of Medicine (IOM) developed a system known as Dietary Reference Intakes • The IOM attempted to determine the RDA for vitamin D • They found no comprehensive studies on: • the relationship between doses of Vitamin D on serum 25-[OH]D • An RDA for 25-[OH]D linked to clinical outcomes • They also found that most studies combined the evaluation of Ca and Vitamin D Background

  4. RDA for Vitamin D is also hard to determine because its supply depends on many factors such as sun exposure, BMI, and skin color • Vitamin D insufficiency is defined as a 25-[OH]D level ≤ 50 nmol/L • Vitamin D is known to act on bone metabolishm and calcium hemostasis • Also theorized that it plays an important role in cellular proliferation and differentiation and survival of cells in disorders of immunity and cancer Background

  5. 1 year, randomized, prospective, placebo-controlled trial • Study was conducted at Creighton University Medical Center (Omaha, Nebraska) Study Design

  6. Inclusion Criteria Exclusion Criteria Comorbid conditions Hx of cancer w/in 10 years Terminal illness Hip fracture BMI < 45 kg/m2 High Ca Low bone density Current use of bisphosphonates • Women • 7 years post-menopausal • White • Age 57-90 • Vitamin D insufficiency Study Design

  7. Patients were randomly assigned to 1 of 7 Vitamin D3 doses or placebo for 1 year • 400 IU/d • 800 IU/d • 1600 IU/d • 2400 IU/d • 3200 IU/d • 4000 IU/d • 4800 IU/d Study Design

  8. Study Design

  9. Primary: • 25-[OH]D and PTH levels after 6 months and 1 year • Secondary: • Levels of serum 1,25-dihydroxyvitamin D3 • Serum Caand creatinine • Urine bone markers • Bone mineral density • Calcium absorption • Incidence of falls • FEV1 • Physical performance tests • Blood pressure • Cellular studies Outcomes

  10. It was determined that every dosage group needed 20 participants to achieve a 90% power to detect a difference between dose groups in a 1 way analysis of variance model • Provides a statistical test of whether or not the means of several groups are all equal, and therefore generalizes t-test to more than two groups Statistics

  11. Mixed-effects models were used to estimate dose-response curves for serum 25-[OH]D and PTH • Mixed models are applied where multiple correlated measurements are made on each unit of interest or repeated measurements are made on the same statistical units, or where measurements are made on clusters of related statistical units. Statistics

  12. Interactions between dose and time were also explored • Covariance structures were compared by using the Akaike information criterion • The compound symmetry structure had similar Akaike information criterion values, so it was chosen Statistics

  13. Vitamin D dose–response curve.Baseline, 6-mo, and final serum 25-(OH)D levels are presented according to dosage of vitamin D or placebo. Gallagher J C et al. Ann Intern Med 2012;156:425-437

  14. Serum 25-(OH)D levels according to vitamin D dosage. Levels are shown with a fitted line by using the mixed-effects model, with 95% bootstrapped limits at 12 mo. 25-(OH)D = 25-hydroxyvitamin D. Gallagher J C et al. Ann Intern Med 2012;156:425-437

  15. Effect of BMI and vitamin D dose on levels of serum 25-(OH)D at 12 months.BMI <25 kg/m2, n = 31; BMI 25.0–29.9 kg/m2, n = 56; and BMI ≥30.0 kg/m2, n = 76. 25-(OH)D = hydroxyvitamin D; BMI = body mass index. Gallagher J C et al. Ann Intern Med 2012;156:425-437

  16. Safety and ADRs

  17. The increased levels of 25-[OH]D were not linear but followed a quadratic curve suggestive of a rate-limiting mechanism • BMI has a significant effect on serum 25-[OH]D levels as well as on the dose of Vitamin D3 • At 12 months there was a significant decrease in serum PTH levels associated with increasing Vitamin D3 doses • The effects of Vitamin D in other diseases have not been established Discussion

  18. Strengths Limitations Sample size was small Healthy, postmenopausal white women only • Double-blind, placebo control • Adequate power • Multiple doses were studied • Length of study Discussion

  19. Gallagher J, Sai A, Templin T, Smith L. Dose response to vitamin d supplementation in postmenopausal women: a randomized trial.Annals Of Internal Medicine [serial online]. March 20, 2012;156(6):425-437. Available from: MEDLINE with Full Text, Ipswich, MA. Accessed March 29, 2012. • Analysis of Variance. Wikipedia. Accessed 20 March 2012. http://en.wikipedia.org/wiki/Analysis_of_variance • Mixed Model. Wikipedia. Accessed 20 March 2012. http://en.wikipedia.org/wiki/Mixed_model • Akaike Information Criterion. Wikipedia. Accessed 20 March 2012. http://en.wikipedia.org/wiki/Akaike_information_criterion References

  20. Serum PTH levels, according to vitamin D dosage at 12 months.PTH = parathyroid hormone. Gallagher J C et al. Ann Intern Med 2012;156:425-437

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