09 Apr Are Today’s Adolescents at Risk for Osteoporosis?
Osteoporosis is a preventable, potentially debilitating disease characterized by low bone density and increased bone fragility that affects millions of people. Dietary intake of calcium, magnesium and vitamin D is critical during this life stage for optimal bone growth; unfortunately, the majority of adolescents in North America do not consume adequate amounts.
In addition, many adolescents are now using oral contraceptives or intrauterine devices that prevent ovulation, thus inhibiting formation of progesterone required for the development of osteoblasts. Oral contraceptives also lower blood levels of vitamins B6 and B12, both of which are necessary to prevent elevated levels of homocysteine, whose impact on bone can be significant. In addition to “the pill,” many commonly prescribed medications disrupt normal bone remodeling and promote osteoporosis. Other remediable factors that cause excessive bone loss include insufficiencies of key nutrients, such as vitamin D3, magnesium, and calcium, required for healthy bone remodeling.
Other life style choices that affect bone health include excessive caffeine and carbonated beverage intake, strict vegetarian diets, smoking, alcohol use as well as eating disorders. It is important to recognize key risk factors and manage those that can be modified to prevent disease and/or minimize risk of fracture. The following is an excerpt from the synopsis of the risks the current North American diet places on developing osteoporosis on later life.
Although the highest incidence of osteoporosis actually appears in menopause and later life stages, prevention best occurs during the adolescent stage when the foundation is laid for bone growth and development. During adolescent years, the skeletal system is highly active in the body, absorbing dietary calcium and providing for the bone mass that will be required for life; 90% of adult bone mass is acquired during adolescence. Although 60–80% of the amount of peak bone mass achieved is predetermined by genetics, the final amount is influenced by environmental, health, and lifestyle factor.
The seeds of this pernicious disease are sown during adolescence, when the skeleton is most active in absorbing dietary calcium and building up nearly all the bone mass that will carry the teenager throughout life. Along with calcium, both magnesium and vitamin D are essential for bone formation. A number of recent investigations have shown a high prevalence of low vitamin D status in the US population, especially in adolescents, during the winter. Little research has been done to evaluate adolescents’ magnesium requirements for optimal bone development, but recent papers indicate that magnesium status plays an important role in children’s bone health.
Vitamin K2 is increasingly being viewed as a necessary vitamin for bone health. Given the abysmally low intake of foods rich in vitamin K in the N. American population, for example, broccoli, leafy greens, and unhydrogenated vegetable oils (hydrogenation detrimentally changes the chemical structure of vitamin K), vitamin K insufficiency in adolescents is very high. Research evaluating vitamin K intake found that only half the females age 13 and over and less than half the males got the recommended daily allowance of vitamin K, which recent evidence suggests is not sufficient for maximizing the function of vitamin K in bones.
Birth Control
Many adolescent females are now using oral contraceptives. Whether a combination of a patented version of estradiol plus progestin or a progestogen-only “mini-pill” is taken, either form of birth control pill inhibits follicular development and prevents ovulation, thus inhibiting production of progesterone, which is primarily produced as a result of ovulation and is required for the development of osteoblasts. Oral contraceptives also lower blood levels of vitamins B6 and B12, both of which are necessary to prevent elevated levels of homocysteine. Homocysteine interferes with collagen crosslinking, and its impact on bone can be significant. In the elderly, elevated levels of homocysteine have been found to increase risk of hip fracture by 70%.
One of the most recently developed contraceptives, now being used in women as young as 14 years of age, is an intrauterine device containing a progestin (levonorgestrel) marketed under the trade name, Mirena® . Mirena not only prevents ovulation but also causes amenorrhea in the majority of the young, premenopausal and perimenopausal women in whom it has been inserted. A recent meta-analysis has estimated a BMD increase of 0.5% per year in women with normal ovulation, but a decrease in BMD of 0.7% per year in young women with ovulatory disturbances (anovulation or short luteal phase). The use of progestins inhibits ovulation. Because the span of years from adolescence when menstruation begins through to the early 30s are the years when women are supposed to be building up peak bone mass, use of progestins may be setting up this generation of young women for early and severe osteoporosis.
Smoking
Studies have suggested that smoking, including passive smoking, is a risk factor for low BMD. The effect of smoking is directly related to the amount smoked (or the amount of second-hand exposure) and body weight, with more frequent users and those with lower body weight having greatest loss of BMD. The mechanisms involved in pathogenesis of osteoporosis in smokers involve multiple changes within the body, including decreased intestinal calcium absorption and alteration of metabolism of several hormones, including calcitropic hormone, estradiol, adrenal corticol hormone, or effects on the RANK-RANKLosteoprotegerin (OPG) system, collagen metabolism, and bone angiogenesis. The effects of two key components in cigarette smoke, cadmium and nicotine, provide insight into smoking and is so detrimental to bone. Cadmium stimulates the formation and activity of osteoclasts and inhibits inactivation of cortisol (chronically elevated cortisol destroys osteocytes). Nicotine depresses osteoblast activity and increases hepatic clearance of estrogen; women who smoke enter menopause up to 2 years earlier than their non-smoking peers.
Carbonated Beverages
Increased intake of carbonated beverages has been seen in recent years. Several studies have investigated the effects of carbonated beverages on BMD and have reported mixed results. Data from over 2,500 men and women who participated in the Framingham Osteoporosis Study were examined and it was found that cola, but not other carbonated beverages, was associated with low BMD in women, but not in men. The mechanisms by which this occurs are not fully understood, but it has been hypothesized that the content of phosphoric acid may play a role. Caffeinated carbonated drinks have stronger associations than decaffeinated beverages with low BMD, possibly due to the effect caffeine has on calcium absorption. Caffeine intake can inhibit the uptake of calcium, therefore reduction of caffeine intake is recommended and should at least be separated from intake of sources of calcium.
Nutritional Recommendations
It is important to raise awareness that prevention of osteoporosis starts in the adolescent years when the body is creating the majority of bone mass that will be required for life. It is of great importance that the nutritional needs of our youths are met to ensure their health in the future. Current dietary habits in North America warrant more attention, particularly with respect to ensuring recommended nutritional requirements are being met and habits such as cola and caffeine consumption is minimized, which puts bone health at risk in future years. For lifelong bone health, it is essential for teenagers – particularly girls – to consume enough calcium, magnesium, vitamin D, B vitamins and potentially vitamin K2 while they are young to achieve their maximum bone density. By the mid-20s the critical window period for calcium absorption starts to close, as a woman’s ability to stock pile this mineral in her bones is greatly reduced. Calcium and dairy intake in Canada and the US is inadequate in 4–18 year olds, with calcium intake reported to be approximately 500 mg/day among this population.
Conclusion
Today, few teenage girls in North America are meeting the recommended dietary guidelines for calcium intake during this period of peak bone mass accrual. The decreased consumption of dairy products has been associated with vitamin D deficiency and increased consumption of carbonated beverages and/or sweetened beverages. Soft drinks are problematic, not only because they have displaced calcium-rich milk as a source of refreshment but also as caffeine (which most sodas contain) impairs absorption and thereby increases the excretion of calcium in the urine, further reducing the calcium available for bone development. As such, soda consumption, especially colas, should be reduced and teenagers should be encouraged to increase intake of low-fat milk and other healthy sources of calcium such as dairy products, fortified juices, and vegetables.
Unfortunately, prevention occurs at an early age when many are not worried about bone health later in life. Although the importance of calcium and vitamin D intake is well understood in the medical community, fewer physicians are aware of the importance of a number of other nutrients shown to play a role in bone health: magnesium,vitamin K2, manganese, zinc, copper, strontium, silicon, folic acid, vitamin B12, phosphorus, and vitamin C. Public awareness and programs to increase intake of these key nutrients and to decrease poor dietary habits during adolescent years is crucial to reducing the prevalence of osteoporosis and decreasing the burden on the healthcare system in future generations.
Published in the J of Restorative Medicine, Osteoporosis: The Need for Prevention and Treatment (excerpt), by Karan Baucom, MD; Lara Pizzorno, MA; and Joseph Pizzorno, ND