Bioinorganic Chemistry: Calcium Functions and Sources

Bioinorganic Chemistry

• Calcium is the most abundant mineral in animal tissues, with 99% found in the skeleton.
• It's found in blood and other tissues and is crucial for bone structure, nerve function, blood clotting, muscle contraction, and cellular metabolism.
• Sources of calcium include milk and dairy products (high amounts, high bioavailability, fortified with vitamin D), green leafy vegetables (poor absorption), fish with bones, and fortified juice/cereal.
• Calcium and phosphorus are both needed for bone formation and other non-skeletal functions, with a dietary ratio of 1:1 to 2:1 beneficial for most animals.
• Calcium absorption depends on vitamin D, intestinal Ca-binding protein, and is influenced by need (high during growth, pregnancy, and lactation), and decreased by phyates (grains) and oxalates (grains).
• Wheat bran, low estrogen levels (postmenopausal women) also decrease bioavailability.
• Factors that enhance calcium absorption include stomach acid, vitamin D, lactose, and growth hormones.
• Factors that inhibit calcium absorption include lack of stomach acid, vitamin D deficiency, high phosphorus intake, high fiber diets, phytates in seeds/nuts/grains, and oxalates in greens.
• Calcium regulation involves plasma Ca, with normal levels at 8-12 mg/dl, and regulation by hormones like vitamin D3 (from the kidney), parathyroid hormone (PTH, from parathyroid gland), and calcitonin (from thyroid gland).
• PTH & vitamin D3 increase plasma Ca, while calcitonin decreases it.
• Calcium deficiencies cause rickets in growing animals, and osteomalacia (osteoporosis) in adults. Parturient paresis (milk fever) affects lactating animals.
• Bone growth is most significant during linear growth, peaking around age 30.
• Around age 40, bone breakdown exceeds formation.
• By age 65, some women experience a 50% loss of bone mass.
• Maintaining adequate calcium and vitamin D intake, weight-bearing exercise, and supplementing estrogen are strategies for preventing osteoporosis.
• Bones are made of osteoblasts, responsible for bone formation, and osteoclasts, responsible for breakdown of older bone.

Macronutrients

• Macronutrients are needed in large quantities to fuel the body and support growth/maintenance.
• Common macronutrients include carbohydrates, proteins, and fats.

Micronutrients

• Micronutrients, including vitamins and minerals, are required in small amounts for normal metabolism, growth, and well-being.
• Minerals encompass microminerals (trace elements like Fe, Cu, F, Zn, I, Se, Mn, Mo, Cr, Co, and B) and macrominerals (Na, Mg, K, Ca, P, S, and Cl).
• Vitamins include A, B, C, D, E, and K.

Minerals

• Minerals are inorganic elemental atoms that are essential nutrients, unaffected by digestion or metabolism.
• Their functions include participation in metabolic processes (cofactors), providing structural components (e.g., Ca, P in bone; S in keratin), and maintaining acid-base and water balance (e.g., Na, K, Cl).
• They also play unique roles, such as in nerve and muscle function, heme, B12, and thyroid hormones.
• Examples of major minerals include Calcium, Phosphorus, Magnesium, Sodium, Chloride, and Potassium.

Bioavailability and Regulation of Major Minerals

• Bioavailability is the proportion of an administered drug dose that enters the systemic circulation.
• Factors influencing bioavailability include genetics, aging, nutritional status, and other food compounds.
• Absorption often occurs in the small and large intestines.
• Regulation occurs in the kidneys and small intestine.

Classification of Minerals

• Macro or Major minerals (Na, K, Mg, Ca, P, Cl) are present in the body tissues at high concentrations (greater than 50 mg/kg or 50 ppm).
• Micro or Trace minerals (Cr, Mn, Fe, Co, I, Se) are present at lower concentrations (less than 50 mg/kg or 50 ppm).

Nutritionally Important Minerals

• A table providing the quantities of macro and trace minerals in g/kg and mg/kg.

Minerals in Foods

• Minerals are found in all food groups, but animal products are more reliable sources.
• Factors like oxalates (spinach) and phytates (grains) can reduce mineral absorption (bioavailability).

Factors Affecting Requirements

• Physiological state/level of production.
• Interactions with other minerals.
• Tissue storage.
• Form fed (inorganic vs organic forms).

Deficiencies and Excesses of Minerals

• Most minerals have an optimal range.
• Levels below the optimal range can lead to deficiency symptoms.
• Levels above the optimal range can lead to toxicity symptoms.
• Mineral content of soils directly affects the mineral status of plants (and animal feeds).
• Deficiency/excess effects may take many months to develop. Development is heavily impacted by body stores of the mineral.

Requirements and Toxicities

• A table showing the requirements and toxic levels of specific minerals (Cu, Co, I, Se) for specific animal species (cattle, swine, etc.).

Phosphorus

• Phosphorus is similar to calcium in function, crucial for energy metabolism (ATP, sugar phosphates).
• It's a component of phosphoproteins and is essential for various bodily functions.
• Deficiencies in phosphorus can lead to rickets or osteomalacia. The deficiency can present as Pica (preference chewing wood/bones), which is a sign of a deprived appetite.
• Deficiencies can impact animal fertility and milk production/growth.

Chromium

• Chromium regulates insulin, growth, and development, and it impacts lean mass and fat mass in lab animals.
• It is an ergogenic aid in some formulations.
• Deficiencies in chromium can cause elevated blood glucose and reduced insulin sensitivity, leading to weight loss.

Manganese

• Manganese acts as a cofactor for metalloenzymes, crucial for gluconeogenesis and bone formation.
• Deficiency is rare and may present as scaly skin, poor bone formation, and/or growth retardation.
• Toxicity is also rare but can be an issue for workers in certain industries or areas with high water content.

Molybdenum

• Molybdenum participates in redox reactions and acts as a cofactor for several enzymes involved in the metabolism of sulfur-containing amino acids and DNA/RNA.
• Deficiency is rare, while toxicity may have impacts on animal reproduction.

Zinc

• Zinc is essential for RNA synthesis, protein stabilization (including zinc fingers), antioxidant function, and cell membrane stability.
• Deficiency may cause a reduced appetite, increased morbidity, and impaired growth, among other symptoms.
• Toxicity from supplements can cause poor immune function and depressed HDL levels.

Fluoride

• Fluoride is crucial to bone and tooth matrix. It promotes calcium and phosphate mineralization and inhibits bacterial growth, thus protecting against dental cavities.
• Deficiency is rarely seen.
• Toxicity symptoms can cause GI upset, excessive saliva production, watery eyes, heart problems, and coma. There are also forms of dental fluorosis and skeletal fluorosis that can be caused by excess fluoride.
• It is not an essential nutrient, but it is often added to drinking water or in toothpaste.

Cobalt

• Cobalt is a noteworthy element related to vitamin B12 synthesis.
• Cobalt deficiencies can cause significant problems in several species of animals.
• It is essential for propionate metabolism and DNA synthesis.

Other Trace Minerals

• The other trace minerals include nickel, aluminum, silicon, vanadium, arsenic, and boron.

Iodine

• Iodine is an essential component of thyroid hormones (T3 and T4).
• Thyroid hormones regulate body temperature, basal metabolic rate, reproduction, and growth.
• Iodine is mainly absorbed in the small intestine and stomach and is taken up by the thyroid gland. Thyroid-stimulating hormone regulates iodine uptake.
• Iodine is mainly absorbed in the small intestine and stomach.
• Deficiency leads to goiter (less severe) and cretinism (severe). Symptoms of both include stunted growth and impaired cognitive function.

Copper

• Copper is essential for the normal absorption, transport, and mobilization of iron and hemoglobin synthesis.
• It is also an important component of many enzymes (e.g., cytochrome oxidase) and is stored primarily in the liver.
• Copper deficiency may result in anemia, depigmentation of hair/wool, loss of wool crimp, bone disorders, and central nervous system lesions.
• Copper toxicity is rare.

Selenium

• Selenium is vital for protecting cells from damage and is a significant antioxidant.
• Selenium deficiencies may cause white muscle disease (in lambs and calves), skeletal and cardiac myopathies (in various animals), and exudative diathesis in chicks.
• Toxicity is possible at high amounts.