Skills to Develop
- Identify additional nutrients that are vital in maintaining bone health and state their primary role.
- Identify food sources for each nutrient.
Bone tissue is greater than 70 percent inorganic material and as such, minerals are important for maintaining skeletal health. In addition to calcium, other minerals critical for bone health are phosphorus, magnesium, and fluoride. Vitamin K is also important to bone health. But that is not all—iron, copper, zinc, and vitamin C are also essential for the synthesis of collagen. Consuming too much or too little vitamin A affects bone health too, as it plays a role in osteoclast and osteoblast activities. The fact that there are many bone-friendly nutrients provides us with one more reason why it is better to eat a diet rich in many nutrients than taking one particular supplement. In Table 9.5.1, notice the important nutrients for bone health and good food sources for each.
|Micronutrient||Functional Role in Bone Health||Food Sources|
||collards, mustard greens, kale, turnips, broccoli, beans, black molasses, and fortified juices, cereals, and milk.|
||non-genetically-modified soy, legumes, whole grains, dairy, nuts, and seeds|
||whole grains and legumes, almonds, cashews, hazelnuts, beets, collards, and kelp|
||fluoridated water, foods prepared in fluoridated water, seafood (because the ocean contains natural sodium flouride)|
||salmon, mackerel, tuna, sardines, mushrooms, cod liver oil, egg yolks, and fortified milk, yogurt, and cheese|
||kale, spinach, turnip, and other dark leafy vegetables|
||avocado, nuts, peanut butter, green and orange vegetables, grapes, and raisins|
||red meat, egg yolks, dark leafy vegetables, dried fruit, iron-fortified foods, beans, lentils, chick peas, liver, and artichoke|
||citrus fruits, tomatoes and tomato juice, potatoes, Brussel sprouts, cauliflower, broccoli, strawberries, cabbage, and spinach|
||oysters, wheat germ, pumpkin seeds, squash, watermelon seeds, beans, sesame seeds, tahini, beef, lamb|
Phosphorus’s Functional Role
Phosphorus is the second most abundant mineral in the human body. Eighty-five percent of it is housed in the skeleton. In addition to serving as a primary mineral in the skeleton, phosphorus in the form of phosphate is a component of the backbones of RNA and DNA, the cellular energy storing molecule, adenosine triphosphate (ATP), and phospholipids. Because phosphorus is present with calcium in mineralized bone, it is somewhat regulated in parallel with calcium. PTH and calcitriol stimulate bone resorption, increasing not only blood levels of calcium but also blood phosphate levels. However, in contrast to the effect of PTH on calcium reabsorption by the kidney, PTH stimulates the renal excretion of phosphate so that it does not accumulate to toxic levels. It is usually found as phosphate or phosphorous salt.
Deficiency signs and symptoms include muscle weakness, loss of appetite (anorexia) and bone pain. A deficiency is rare but more apt to be found in preterm infants, elderly individuals, excess alcohol intake and postmenopausal women.
Dietary Reference Intake and Food Sources for Phosphorus
In comparison to calcium, most Americans are not at risk for having a phosphate deficiency. Phosphate is present in many foods popular in the American diet including meat, fish, dairy products, processed foods, and beverages. Phosphate is added to many foods because it acts as an emulsifying agent, prevents clumping, improves texture and taste, and extends shelf-life. The average intake of phosphorus in US adults ranges between 1,000 and 1,500 milligrams per day, well above the RDA of 700 milligrams per day. The UL set for phosphorous is 4,000 milligrams per day for adults and 3,000 milligrams per day for people over age seventy.
|Age Group||RDA (mg/day)||UL (mg/day)|
|Infants (0–6 months)||100*||–|
|Infants (6–12 months)||275*||–|
|Children (1–3 years)||460||3,000|
|Children (4–8 years)||500||3,000|
|Children (9–13 years)||1,250||4,000|
|Adolescents (14–18 years)||1,250||4,000|
|Adults (19–70 years)||700||4,000|
|Adults (> 70 years)||700||3,000|
|* denotes Adequate Intake|
|Foods||Calcium (mg)||Phosphorus (mg)|
|Yogurt, whole milk||121||95|
|Cottage cheese, low-fat||69||151|
|Beef, round steak||7||199|
|Wheat flour, white||15||108|
|Au gratin potatoes||83||95|
|Fast food hamburger||46||97|
|Chocolate cake mix||150||270|
|Chocolate wafer cookies||31||32|
Source: Adapted from US Department of Agriculture National Nutrient Database. Last modified November 1, 2012. www.nal.usda.gov/fnic/foodcomp/search/.
Magnesium’s Functional Role
Magnesium is another major mineral and our bodies contain approximately 25 grams. Approximately 60 percent of magnesium in the human body is stored in the skeleton, making up about 1 percent of mineralized bone tissue. Magnesium is not an integral part of the hydroxyapatite crystal, but it does reside on the surface of the crystal and helps crystal formation to maximize bone structure. Observational studies link magnesium deficiency with an increased risk for osteoporosis. A magnesium-deficient diet is associated with decreased levels of parathyroid hormone and the activation of vitamin D, which may lead to an impairment of bone remodeling. A study in nine hundred elderly women and men did show that higher dietary intakes of magnesium correlated to an increased BMD in the hip.Tucker, K. L. et al. “Potassium, Magnesium, and Fruit and Vegetable Intakes Are Associated with Greater Bone Mineral Density in Elderly Men and Women.” Am J Clin Nutr 69, no. 4 (1999): 727–36. Only a few clinical trials have evaluated the effects of magnesium supplements on bone health and their results suggest some modest benefits on BMD.
In addition to participating in bone maintenance, magnesium has several other functions in the body. In every reaction involving the cellular energy molecule, ATP, magnesium is a required cofactor. More than three hundred enzymatic reactions require magnesium. Magnesium plays a role in the synthesis of DNA and RNA, carbohydrates, and lipids, and is essential for nerve conduction, muscle contraction, and blood clotting. Another health benefit of magnesium is that it may decrease blood pressure.
Dietary Reference Intake and Food Sources for Magnesium
The RDAs for magnesium for adults between ages nineteen and thirty are 400 milligrams per day for males and 310 milligrams per day for females. For adults above age thirty, the RDA increases slightly to 420 milligrams per day for males and 320 milligrams for females.
Figure 9.5.1: For optimal magnesium intake, try consuming whole-grain breads and cereals. (Public domain; Peggy Greb, USDA ARS)
|Age Group||RDA (mg/day)||UL (mg/day)|
|Infants (0–6 months)||30*||–|
|Infants (6–12 months)||75*||–|
|Children (1–3 years)||80||65|
|Children (4–8 years)||130||110|
|Children (9–13 years)||240||350|
|Adolescents (14–18 years)||410||350|
|Adults (19–30 years)||400||350|
|Adults (> 30 years)||420||350|
|* denotes Adequate Intake Source: National Institutes of Health, Office of Dietary Supplements. “Dietary Supplement Fact Sheet: Magnesium.” Last reviewed July 13, 2009. http://ods.od.nih.gov/factsheets/Magnesium-HealthProfessional/.|
Magnesium is part of the green pigment, chlorophyll, which is vital for photosynthesis in plants; therefore green leafy vegetables are a good dietary source of magnesium. Magnesium is also found in high concentrations in fish, dairy products, meats, whole grains, and nuts. Additionally chocolate, coffee, and hard water contain a good amount of magnesium. Most people in America do not fulfill the RDA for magnesium in their diets. Typically, Western diets lean toward a low fish intake and the unbalanced consumption of refined grains versus whole grains.
A deficiency in magnesium causes hypomagnesemia or low levels of magnesium in the blood which is often accompanied by a low blood calcium and potassium levels. Hypomagnesium is associated with long-term use of protein inhibitor drugs commonly used to treat GERD. Muscle cramps, spasms, nausea, weakness, irritability, and confusion are also symptoms of a magnesium deficiency. Groups at risk for developing a magnesium deficiency are individuals with renal disease, chronic diarrhea, chronic alcohol abuse and elderly people.
A high intake of magnesium is not toxic but pharmacological doses beyond the upper limit can cause diarrhea, nausea, abdominal cramps, pH imbalances, massive dehydration, cardiac arrest, and death. The excessive use of antacids can cause hypermagnesemia that affects kidney functions and impairs nerve, muscle and heart function.
Fluoride’s Functional Role
Fluoride is a water soluble anion. It is known mostly as the mineral that combats tooth decay and is bound to fluoro-hydroxyapatite. It assists in tooth and bone development and maintenance. Fluoride combats tooth decay via three mechanisms:
- Blocking acid formation by bacteria
- Preventing demineralization of teeth
- Enhancing remineralization of destroyed enamel
Fluoride was first added to drinking water in 1945 in Grand Rapids, Michigan; now over 60 percent of the US population consumes fluoridated drinking water. The Centers for Disease Control and Prevention (CDC) has reported that fluoridation of water prevents, on average, 27 percent of cavities in children and between 20 and 40 percent of cavities in adults. The CDC considers water fluoridation one of the ten great public health achievements of the twentieth century.Centers for Disease Control. “10 Great Public Health Achievements in the 20th Century.” Morbidity and Mortality Weekly Report 48, no. 12 (April 2, 1999): 241–43. www.cdc.gov/about/history/tengpha.htm. The optimal fluoride concentration in water to prevent tooth decay ranges between 0.7–1.2 milligrams per liter. Exposure to fluoride at three to five times this concentration before the growth of permanent teeth can cause fluorosis, which is the mottling and discoloring of the teeth. Inadequate intake of fluoride has been linked to dental caries with poor mouth hygiene. People who drink water that is not fluoridated or use toothpaste with no fluoridation, are at a greater risk of developing the signs of a fluoride deficiency. Excess amounts of fluoride are toxic and cause fluorosis.
Fluoride’s benefits to mineralized tissues of the teeth are well substantiated, but the effects of fluoride on bone are not as well known. Fluoride is currently being researched as a potential treatment for osteoporosis. The data are inconsistent on whether consuming fluoridated water reduces the incidence of osteoporosis and fracture risk. Fluoride does stimulate osteoblast bone building activity, and fluoride therapy in patients with osteoporosis has been shown to increase BMD. In general, it appears that at low doses, fluoride treatment increases BMD in people with osteoporosis and is more effective in increasing bone quality when the intakes of calcium and vitamin D are adequate. The Food and Drug Administration has not approved fluoride for the treatment of osteoporosis mainly because its benefits are not sufficiently known and it has several side effects including frequent stomach upset and joint pain. The doses of fluoride used to treat osteoporosis are much greater than that in fluoridated water.
Dietary Reference Intake and Food Sources for Fluoride
The IOM has given Adequate Intakes (AI) for fluoride but has not yet developed RDAs. The AIs are based on the doses of fluoride shown to reduce the incidence of cavities, but not cause dental fluorosis. From infancy to adolescence, the AIs for fluoride increase from 0.01 milligrams per day for ages less than six months to 2 milligrams per day for those between the ages of fourteen and eighteen. In adulthood, the AI for males is 4 milligrams per day and for females is 3 milligrams per day. The UL for young children is set at 1.3 and 2.2 milligrams per day for girls and boys, respectively. For adults, the UL is set at 10 milligrams per day. Greater than 70 percent of a person’s fluoride comes from drinking fluoridated water when they live in a community that fluoridates the drinking water. Other beverages with a high amount of fluoride include teas and grape juice. Solid foods do not contain a large amount of fluoride. Fluoride content in foods depends on whether it was grown in soils and water that contained fluoride or cooked with fluoridated water. Canned meats and fish that contain bones do contain some fluoride.
|Age Group||AI (mg/day)||UL (mg/day)|
|Infants (0–6 months)||0.01||0.7|
|Infants (6–12 months)||0.50||0.9|
|Children (1–3 years)||0.70||1.3|
|Children (4–8 years)||1.00||2.2|
|Children (9–13 years)||2.00||10.0|
|Adolescents (14–18 years)||3.00||10.0|
|Adult Males (> 19 years)||4.00||10.0|
|Adult Females (> 19 years)||3.00||10.0|
Source: Institute of Medicine. Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. January 1, 1997. www.iom.edu/Reports/1997/Dietary-Reference-Intakes-for-Calcium-Phosphorus-Magnesium-Vitamin-D-and-Fluoride.aspx.
Vitamin K’s Functional Role
Vitamin K refers to a group of fat-soluble vitamins that are similar in chemical structure. They act as coenzymes and have long been known to play an essential role in blood coagulation. Without vitamin K, blood would not clot. Vitamin K is also required for maintaining bone health. It modifies the protein osteocalcin, which is involved in the bone remodeling process. All the functions of osteocalcin and the other vitamin K-dependent proteins in bone tissue are not well understood and are under intense study. Some studies do show that people who have diets low in vitamin K also have an increased risk of bone fractures.
Dietary Reference Intake and Food Sources for Vitamin K
The AI of vitamin K for adult females is 75 micrograms per day, and for males, it is 120 micrograms per day. A UL for vitamin K has not been set. Vitamin K is present in many foods. It is found in highest concentrations in green vegetables such as broccoli, cabbage, kale, parsley, spinach, and lettuce. Additionally, vitamin K can be synthesized via bacteria in the large intestine. The exact amount of vitamin K synthesized by bacteria that is actually absorbed in the lower intestine is not known, but likely contributes less than 10 percent of the recommended intake. Newborns have low vitamin K stores and it takes time for the sterile newborn gut to acquire the good bacteria it needs to produce vitamin K. So, it has become a routine practice to inject newborns with a single intramuscular dose of vitamin K. This practice has basically eliminated vitamin K-dependent bleeding disorders in babies.
|Age Group||RDA (mcg/day)|
|Infants (0–6 months)||2.0*|
|Infants (6–12 months)||2.5*|
|Children (1–3 years)||30|
|Children (4–8 years)||55|
|Children (9–13 years)||60|
|Adolescents (14–18 years)||75|
|Adult Males (> 19 years)||120|
|Adult Females (> 19 years)||90|
|* denotes Adequate Intake. Source: Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. January 9, 2001. www.iom.edu/Reports/2001/Dietary-Reference-Intakes-for-Vitamin-A-Vitamin-K-Arsenic-Boron-Chromium-Copper-Iodine-Iron-Manganese-Molybdenum-Nickel-Silicon-Vanadium-and-Zinc.aspx.|
Phosphorous is a primary mineral component of bone, is regulated in parallel with calcium, and in high amounts is detrimental to bone health. Magnesium helps keep bones strong. A deficiency in magnesium can compromise bone health. Fluoride combats tooth decay and benefits teeth and bones when present in the diet at the recommended intake. Vitamin K is a coenzyme that participates in the modification of proteins that act in bone tissues and promotes normal blood clotting.
- Discuss and plan a dinner menu that specifically contains bone-friendly foods. What are you going to serve? Be sure to include enough bone-friendly foods for the different types of vegetarians.
- Discuss some of the functional roles that magnesium, phosphorous, fluoride, and vitamin K serve in the body. In the midst of a busy schedule, how can you ensure you are eating the right amount of foods to provide an adequate supply of these nutrients?