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9.4 Other Essential Micronutrients for Bone Health: Phosphorous, Magnesium, Fluoride, and Vitamin K

Learning Objectives

  1. Identify additional nutrients that are vital in maintaining bone health and state their primary role.
  2. 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 take one particular supplement. In Table 9.4 "Micronutrients and Bone Health", notice the important nutrients for bone health and good food sources for each.

Table 9.4 Micronutrients and Bone Health

Micronutrient Functional Role in Bone Health Food Sources
Calcium
  • Component of mineralized bone
  • Provides structure and microarchitecture
collards, mustard greens, kale, turnips, broccoli, beans, black molasses, and fortified juices, cereals, and milk.
Phosphorus
  • Component of mineralized bone
  • Provides structure and microarchitecture
non-genetically-modified soy, legumes, whole grains, dairy, nuts, and seeds
Magnesium
  • Component of mineralized bone
  • Provides structure and microarchitecture
whole grains and legumes, almonds, cashews, hazelnuts, beets, collards, and kelp
Fluoride
  • Component of mineralized bone
  • Provides structure and microarchitecture
  • Stimulates new bone growth
fluoridated water, foods prepared in fluoridated water, seafood (because the ocean contains natural sodium flouride)
Vitamin D
  • Critical for maintaining calcium levels
  • Aids the absorption of calcium, promotes bone health
salmon, mackerel, tuna, sardines, mushrooms, cod liver oil, egg yolks, and fortified milk, yogurt, and cheese
Vitamin K
  • Stimulates bone remodeling
kale, spinach, turnip, and other dark leafy vegetables
Boron
  • May enhance calcium absorption and estrogen metabolism
avocado, nuts, peanut butter, green and orange vegetables, grapes, and raisins
Iron
  • Helps enzymes and regulators function properly so the body can form optimal bone structure for bone strength
red meat, egg yolks, dark leafy vegetables, dried fruit, iron-fortified foods, beans, lentils, chick peas, liver, and artichoke
Vitamin C
  • Helps enzymes and regulators to function properly so the body can form optimal bone structure for bone strength
citrus fruits, tomatoes and tomato juice, potatoes, Brussel sprouts, cauliflower, broccoli, strawberries, cabbage, and spinach
Zinc
  • Helps enzymes and regulators to function properly so the body can form optimal bone structure for bone strength
oysters, wheat germ, pumpkin seeds, squash, watermelon seeds, beans, sesame seeds, tahini, beef, lamb

Phosphorus’s Functional Role

PhosphorusA mineral that makes up a substantial part of mineralized bone tissue. The dietary sources are meat, fish, and dairy products, as well as processed foods, and cola beverages. 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 to 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.

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.

Table 9.5 Dietary Reference Intakes for Phosphorus

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

Table 9.6 Calcium and Phosphorus Contents in 100 Grams of Certain Foods

Foods Calcium (mg) Phosphorus (mg)
Dairy Products
Buttermilk 116 89
Milk, nonfat 123 101
Milk, whole 207 158
Yogurt, low-fat 199 157
Yogurt, whole milk 121 95
Cottage cheese, low-fat 69 151
Swiss cheese 791 567
Meats
Beef, round steak 7 199
Chicken 15 216
Crab 59 175
Oysters 62 159
Legumes/Nuts
Macadamia nuts 85 188
Soybeans 145 158
Lentils 19 180
Lima beans 21 74
Vegetables
Broccoli 47 66
Carrots 27 44
Lettuce, iceberg 19 20
Parsley 140 60
Cereals/Grains
Barley 32 309
Wheat flour, white 15 108
Oat bran 10 119
Rice, brown 10 77
Rice, white 19 55
Processed Foods
American cheese 712 923
Au gratin potatoes 83 95
Fish sticks 26 182
Fast food hamburger 46 97
Chocolate cake mix 150 270
Chocolate wafer cookies 31 32
Granola bar 105 230
Carbonated Beverages
Cola 2 11
Clear soda 2 0

Magnesium’s Functional Role

Approximately 60 percent of magnesiumA mineral that is part of mineralized bone tissue. The dietary sources are meat, fish, dairy products, whole grains, nuts, chocolate, and coffee. 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 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 ClinNutr 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 required. 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 and muscle contraction. Another health benefit of magnesium is that it may decrease blood pressure.

Dietary Reference Intake and Food Sources for Magnesium

For optimal magnesium intake, try consuming whole-grain breads and cereals.

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.

Table 9.7 Dietary Reference Intakes for Magnesium

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

Magnesium is part of the green pigment, chlorophyll, which is vital for photosynthesis in plants; therefore green leafy vegetables are a good dietary source for 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.

Fluoride’s Functional Role

FluorideA mineral that blocks tooth decay and is part of mineralized bone tissue. The primary dietary source is fluoridated water. is known mostly as the mineral that combats tooth decay. It assists in tooth and bone development and maintenance. Fluoride combats tooth decay via three mechanisms:

  1. Blocking acid formation by bacteria
  2. Preventing demineralization of teeth
  3. 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 in 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. http://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.

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.

Table 9.8 Dietary Reference Intakes for 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

Vitamin K’s Functional Role

Vitamin KA vitamin that acts as a coenzyme that modifies proteins important for bone health. The dietary sources are green vegetables such as broccoli, cabbage, kale, parsley, spinach, and lettuce. 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 for 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.

Table 9.9 Dietary Reference Intakes for Vitamin K

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

Key Takeaways

  • 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.

Discussion Starters

  1. 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.
  2. 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?