Bone Density

Usually thought of as a concern of the middle-aged and the elderly, bone health should be an important consideration throughout a person’s life because the structure and function of your bones play a huge role in the health and stability of your muscles, joints, and tendons.

Bones change on a continuous basis throughout life. Otherwise known as bone metabolism or remodeling, this ongoing process involves removal of old bone from the skeleton (called resorption) and the depositing of new bone (called ossification). Bone remodeling takes place every day, and especially when bone is in need repair, such as after a fracture or injury, or from micro-damage during strenuous activity.

Although bones are constantly being broken down and built up, the pace at which bone remodeling occurs changes with aging.

The highest rate of bone remodeling occurs in your youngest years. By age one, 100 percent of a baby’s bone may have been replaced. When a person reaches adulthood, only about 10 percent of their bone remodels each year. This is why a broken bone in a baby might only take weeks to heal, while the same broken bone in an adult could take months or more.

How does bone remodeling occur?

Bone is remodeled and maintained primarily by two types of cells: osteoblasts and osteoclasts. While osteoblasts build or create new bone, the osteoclasts are involved with the breaking down (resorption) of old bone. This ongoing bone metabolism relies on complex signaling pathways and control mechanisms governed by a group of hormones, minerals, and other cells that achieve the proper rate of growth and differentiation. If these hormones and cells don’t function properly, along with adequate protein and minerals, then bone remodeling, and ultimately bone health, will be impacted.

What hormones are involved?

Parathyroid hormone (PTH), a hormone made in the parathyroid gland, is secreted in response to low levels of calcium in the blood. PTH indirectly stimulates osteoclasts to pull calcium from the bones to increase calcium in the blood. To maintain calcium levels in the blood and keep PTH at bay, nutritional intake of calcium is important.

Calcitonin, a hormone produced in the thyroid gland, is also involved in regulating calcium and phosphate levels in the blood, and works opposite to PTH. Calcitonin lowers blood calcium levels by reducing osteoclast activity in the bones and helping your body rid itself of excess calcium by releasing some in your urine. Also important in this homeostasis process is vitamin D. Through several conversions in your skin, liver, and kidneys, the active form of vitamin D acts like a hormone by regulating the concentration of calcium and phosphate, thereby positively impacting bone growth.

Growth hormone, produced by the anterior pituitary gland in the brain, is an anabolic hormone that controls the growth of many cells in the body, including bone. It also plays a role in calcium retention and supports the supplying of minerals into your bones.

As we age, osteoblastic activity – cells creating new bone – decreases, resulting in more bone being broken down than bone being replaced. This is what results in age-related loss of bone mass.¹

What can weaken bones?

A poor diet, including very low-calorie intake or not eating nutrient-dense foods, contributes to weakened bones. A diet high in sodium, sugar, caffeine, and carbonated beverages with phosphoric acid will all leach calcium from the bones.

A history of smoking and a sedentary lifestyle are two modern-day factors that contribute to low bone density. Coupled with a body weight that is either too low or too high, these three factors can decrease bone mineral density by as much as 20 percent compared to individuals who maintain a normal weight, do not smoke, and are physically active throughout their adult years.² Why does being overweight impact bone density? Overweight individuals tend to be deficient in vitamin D, which is necessary for calcium absorption. Younger females can be underweight because they engage in extreme exercise and/or restrict food intake, which can result in lack of menstruation, which impacts the ability to regulate mineral levels in the body and contributes to bone mineral loss at an early age.

Prescription medications also play a role in bone health. Steroids and anti-seizure medications can cause rapid bone mineral loss, especially when used at high doses over an extended period of time.

There are several risk factors for low bone density that can’t be controlled, including age, genetics, and ethnicity. Females older than 50 because of a decrease of estrogen and/or testosterone, men or women with a family history of osteoporosis, and being of Anglo-Saxon or Asian descent are all risk factors for osteoporosis. Disease conditions like diabetes and celiac disease can increase the risk for low bone density. And don’t be fooled if you’re a man – men get osteoporosis too.

How do you know if you have weakened bones?

Osteoporosis is the most common bone condition – the bones become more porous and less dense. Low bone density doesn’t usually have symptoms, at least not in the early stages. The first sign you have a problem might be a fracture. Other outward signs can include bone pain or the appearance of a curved spine in the upper back that causes a hump. Diagnosis is typically done with a bone scan called dual-energy x-ray absorptiometry, a non-invasive test that measures bone density and can measure even the slightest changes in bone mass density.

What can you do to support bone health?

Your diet should contain sufficient nutrient-dense calories, and plenty of specific nutrients like protein, the omega-3 fatty acids EPA and DHA, vitamins D and K, and the minerals calcium and magnesium, as well as other vitamins and minerals necessary for bone remineralization.

Although a higher body weight is associated with greater bone mineral density, the distribution and composition of the weight can make a difference. Individuals who weigh more tend to have greater mechanical loading on their bones and joints, which means that merely walking down a flight of stairs places an exercise-like stress effect on bone hormones and other signals associated with exercise, leading to improved bone density. However, weight from body fat, particularly abdominal obesity, can have a negative impact. The best bet is to maintain a healthy weight for your size and body composition.

Exercise can be of benefit

Resistance exercise benefits the bone remodeling process. And while resistance exercise in the water has less impact on joints, the mechanical movements of your joints and bones on land – jumping, running, and weight-lifting, for example, can have profound positive impacts on the cells and hormones used in the bone remodeling process. It is never too late to start exercising to see these benefits.³

Get proper sleep and sun exposure. Less sleep duration is closely associated with lower bone mineral density in middle-aged and senior women.⁴ Sun exposure will not only help you regulate your sleep-wake cycles, but will also support healthy vitamin D levels.

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References

1. Sheu Y, Cauley J. The role of bone marrow and visceral fat on bone metabolism. Curr Osteoporos Rep 2011;9(2):67-75.
2. Wilsgaard T, Emaus N, Ahmed L, et al. Lifestyle impact on lifetime bone loss in women and men: the Tromsø Study. Am J Epidemiol 2009;169(7):877-886.
3. Cadore E, Brentano M, Kruel L. Effects of physical activity on bone mineral density and bone remodelation. Rev Brasil Med Esporte 2005;11(6):373-379.
4. Fu X, Zhao X, Lu H, et al. Association between sleep duration and bone mineral density in Chinese women. Bone 2011;49(5):1062-1066.