2 Calcium.pdf

HNUT10010 HNUT10020 Human Nutrition 1: Understanding Nutrients Aifric O’Sullivan BSc, MSc, PhD UCD Institute of Food and Health School of Agriculture and Food Science Calcium • Most abundant mineral in the body (1200g) • Majority of body’s calcium is in bones and teeth (99%) – Part of bone struct...

HNUT10010 HNUT10020 Human Nutrition 1: Understanding Nutrients Aifric O’Sullivan BSc, MSc, PhD UCD Institute of Food and Health School of Agriculture and Food Science Calcium • Most abundant mineral in the body (1200g) • Majority of body’s calcium is in bones and teeth (99%) – Part of bone structure – Calcium bank • Body fluids (1%) – Blood – Extracellular fluid – Muscle and other tissues National Adult Nutrition Survey - Calcium Foods That Contribute to Calcium Intake in Ireland Foods Supplying ~200 mg Calcium • ~125mls milk • Small piece of cheddar cheese 28g • 1 small carton yoghurt • 1.5 cartons of cottage cheese 225 ml • A serving of canned sardines 56 g • 6 medium slices of white or brown bread Calcium RDA 1-10 years 11-17 years 18+ years Pregnancy Lactation¶ EFSA PRI 1000mg • 5 – 6 servings of green leafy vegetables 550g What is your daily calcium intake? mg/d 800 1200 800 1200 1200 Calcium Absorption and Metabolism 1000 mg Ca small intestine 1 2 Active + 300 mg (30%) Passive Concentration dependent 100 mg digestive juices etc. 800 mg Deposition Vitamin D dependent Resorption Plasma Ca+ 9-10.4 mg/100 ml 60 mg  + 200 mg Physiological factors: vitamin D status, pregnancy, age Dietary factors: oxalates and phytates in foods – Table 9.1 Calcium Absorption and Metabolism • Calcium concentrations are tightly controlled • Whenever blood calcium levels fall too low or rise too high, 3 systems respond – Intestines, bones and kidneys • Vitamin D, parathyroid hormone (PTH), calcitonin serve to increase or decrease plasma concentrations Calcium Balance Rising blood calcium signals release of calcitonin Plasma Ca+ 9-10.4 mg/100 ml Falling blood calcium signals release of PTH Calcitonin inhibits vitamin D PTH stimulates vitamin D Calcitonin prevents reabsorption PTH + D stimulate Ca reabsorption Calcitonin limits absorption Vitamin D enhances absorption Calcitonin inhibits resportion PTH + D stimulate resportion These actions lower blood calcium which inhibits calcitonin secretion These actions raise blood calcium which inhibits PTH secretion Calcium Metabolism High blood calcium Bone formation Low blood calcium Bone demineralisation Calcitonin Blood Ca2+ Vitamin D PTH Osteoclasts Ca2+ mobilization Osetoblasts Ca2+ uptake Blood Ca2+ Ca2+ Increased Ca2+ excretion in urine Decreased Ca2+ reabsorption Ca2+ PTH Vitamin D Ca2+ Calcium Metabolic Function More than just bones and teeth • Extraskeletal calcium – Vascular contraction and vasodilation – Muscle contraction – Nerve transmission – Blood clotting • Click here to watch a short video describing the role of calcium in muscle contraction Calcium Metabolic Function • Normal skeletal growth – – – – Bone turnover/remodeling is continuous Formation exceeds breakdown in periods of growth Early /middle adulthood both processes are relatively equal Aging adult, bone breakdown exceeds formation Adequate calcium intake is essential for PBM 150 mg/day Bone loss associated with fractures Calcium Status Dual-energy X-ray absorptiometry - DEXA • Bone Mineral Content • Bone Mineral Density (BMC/Area) Osteoporosis WHO Definition • Normal: BMD within 1 SD of the young adult reference mean for the population • Osteopenia: BMD between −1 and −2.5 SD of the young adult mean • Osteoporosis: BMD more than −2.5 SD below the young adult mean Calcium Status • Toxicity – – – – – US UL 2500 mg/day Kidney stones Calcification of soft tissue Absorption of minerals (Fe, Zn) Linked to supplement use • Deficiency – Reduced bone mass – Osteoporosis Reading • Gibney M, Lanham-New S, Cassidy A, Vorster H, eds. Introduction to Human Nutrition. 2nd ed: Wiley-Blackwell, 2009. Chapter 9 • Gropper SS, Smith JL. Advanced Nutrition and Human Metabolism, International Edition 6th ed: Wadsworth Cenage Learning, 2013. Chapter 11-13 • Whitney E, Rolfes SR. Understanding Nutrition, 13th Edition: Wadsworth, Cengage Learning, 2013. Chapter 12-13