The bones that provide the human body with form and structure and allow us to move with speed and grace are part of a complex and metabolically active system. The bones are a matrix of protein filled in with minerals, principally calcium, the most abundant mineral in the body.
Bone development occurs in three distinct stages. From birth to age two, the bones grow rapidly. Throughout childhood and adolescence, this growth continues in spurts, eventually slowing to a halt in the late teens and early twenties. This is not the end of bone development however, merely the end of the lengthening stage.
It's now time for the addition of shape and thickness, called the modeling stage (also referred to as consolidation). Bones acquire mass and are shaped and molded in response to the stresses marked by youthful exuberance, hanging from bars, falling out of trees, and rolling in the mud.
The final stage is remodeling, a combination of breakdown (resorption, a kind of dissolving of the bone as the body reclaims minerals) and reformation that occurs throughout life. By about mid-30s for most people, the rate of bone resorption begins to exceed the rate of bone formation, leading to the inevitable loss of bone mass, which includes proteins and minerals.
There are many factors, including genetics, that determine the rate of bone loss as we age. Weight-bearing exercise and calcium intake, while not the only factors to fight bone mass loss, are good places to start because they illustrate an often ignored point.
It's natural to think of calcium as the major mineral upon which bone health depends. While that picture is true, it's viewed from the perspective of the bone. However, the body's needs for calcium are immediate. Weight-bearing exercises along with all forms of muscle contraction, both voluntary and involuntary, are immediately dependent upon calcium in the blood. The body goes to great lengths to ensure a steady calcium supply to muscles and nerves and thus a consistent blood calcium level. Also, a change in blood pH may require calcium as a buffer. The bones act as a calcium repository that responds to the immediate needs of the blood.
From the perspective of the blood, the immediate needs of calcium can be met by the calcium held in the bones or by dietary calcium, the calcium absorbed through the small intestines. Thus a healthy intake of dietary calcium spares the bones from releasing their calcium store.
Affecting calcium absorption, and thus bone health, is vitamin D. When blood calcium is low, the parathyroid goes into action secreting parathyroid hormone (PTH), which uses three strategies to restore blood calcium. The first is to increase calcium absorption from diet. This involves the activation of vitamin D. The second is to decrease calcium excretion through the kidneys. And the third is to recall calcium from the bone.
Few foods are rich in vitamin D. While sunshine helps the body produce vitamin D, the concern about UV-related skin cancer causes people to lessen their sun exposure. So, many people are at risk for vitamin D deficiency. This not only affects potential bone health but also the many other systems that depend on vitamin D.
"According to the World Health Organization (WHO), osteoporosis ranks second to cardiovascular disease in terms of its global healthcare burden," says Cathy Arnold, supervisor and senior formulation scientist at Fortitech, Inc., Schenectady, N.Y. "Worldwide, the U.S. has the most developed bone and joint health market, which is expected to approach $4 billion by 2013. The functional ingredients market that supports bone and joint health is also a billion dollar industry in China and Japan," she says.
Magnesium (Mg) is a major mineral important for energy metabolism and nerve transmission. A deficiency may impair secretion of PTH and thus the activation of vitamin D. Over half of total body Mg is found in bone where it enhances the crystalline structure.
Low dietary magnesium is common in the U.S. population, especially among children, and it has therefore been suggested that magnesium deficiency could impair bone mineralization. Though most studies fail to show a strong link between magnesium and bone density, a recent study presents evidence that magnesium supplements may reduce bone loss over time, compared to controls.
In addition to minerals, certain vitamins also are important to the structure and function of bones. For example, the protein matrix that constitutes the scaffolding all bone is itself composed mostly of collagen, the integrity of which is highly dependent upon vitamin C status. Vitamin C allows the collagen protein to form a strong triple helix structure upon which minerals are deposited.
Vitamin K status is often a marker of vegetable intake. Vitamin K is noted for its role in blood clotting where it helps make a specific protein good at binding calcium. There are in fact several calcium-binding proteins in bone. Vitamin K itself occurs in two forms: K1 (phylloquinone) in foods and K2 (menaquinone), which is produced by bacteria in the gut.
Essential nutrients may not be the only factors involved in bone health. Antioxidants in green tea, phytoestrogens in soy and other phytochemicals under study and yet to be discovered may also play positive roles in maintaining bone health.
This article originally appeared in the June 2013 issue of Food Processing Magazine.