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Strong, fracture-resistant bones depend on a continuous process of bone turnover and renewal called remodeling, in which old parts of the skeleton are broken down and removed by cells called osteoclasts and replaced with new bone by bone-building cells called osteoblasts. A similar process occurs in most tissues in the body, like skin and hair.

However, many medical conditions can disrupt this delicate balance or impair the absorption of nutrients essential for healthy bone -- i.e., calcium, vitamin D, and protein.

Osteoporosis is typically due to the age-related drop in estrogen levels in women around menopause and a decade or so later in men with waning levels of the male sex hormone testosterone. These reproductive hormones are crucial for building and maintaining bone density. But many common diseases are linked to a higher risk of developing fragile bones -- and some of these are prevalent in young people.

If you are being treated or have been treated for any of the following conditions, or if you have used corticosteroid drugs over a long period, discuss your bone health with your doctor. Even if you are young, an early bone density test and preventive medical treatment may be in order.

In the meantime, be sure to eat a diet rich in calcium and vitamin D, take calcium and vitamin D supplements as directed, and have your blood levels of vitamin D1 checked. Avoid smoking and excess consumption of alcohol and get plenty of weight-bearing exercise.

Autoimmune diseases

Many autoimmune conditions -- those in which abnormalities in a person's immune system cause it to attack tissues -- produce high and widespread levels of inflammation in the body. Some non-autoimmune inflammatory diseases, however, also pose a risk.

Inflammation itself is harmful to the skeleton because it speeds up the breakdown of bone. Furthermore, long-term use of corticosteroid drugs such as prednisone, widely used to treat inflammatory diseases, can interfere with the laying down of healthy new bone by slowing the activity of the body's osteoblasts. This can also decrease absorption of calcium from the intestine, as well as increase calcium loss in urine.

Because these conditions can occur at an early age, they may prevent young persons from reaching their peak bone density in their 20s and early 30s. Reaching that maximum is crucial for preventing bones from becoming thin, fragile, and fracture-prone later in life.

Asthma

The corticosteroids used in inhalers to treat the widespread inflammatory lung condition of asthma -- as well as emphysema, another lung condition -- can increase the risk of bone loss and raise osteoporosis risk in young persons.

And since breathing problems often curtail physical activity, some asthma patients may get less than the amount of weight-bearing exercise necessary for bone strength.

Eczema

This common inflammatory skin disorder is also associated with a higher risk of low bone density and fractures. In addition, the use of very strong topical steroid treatments for severe eczema can interfere with healthy bone remodeling.

Digestive Disease

Celiac disease is an intestinal condition that results from an allergy to gluten, a protein in certain grains, including wheat. Gluten can damage the lining of the intestines, making them less able to absorb nutrients crucial for bone health such as protein, calcium, and vitamin D. This malabsorption can contribute to low bone density even in young people.

Diabetes

Both type 1 and type 2 conditions are associated with negative changes in bone structure, leading to an increased risk of hip and other fractures and delayed healing.

Hyperthyroidism

The thyroid gland regulates metabolism and growth and helps maintain bone. In some cases this gland makes too much thyroid hormone, thus speeding up bone breakdown and loss.

Chronic Kidney Disease

Damaged kidneys can lead to low bone turnover and bone fragility. Impaired kidneys are less able to efficiently remove phosphorus from the blood, and the buildup of this mineral lowers normal levels of calcium. In response, the thyroid gland releases a substance called parathyroid hormone, which removes calcium from bone to correct the imbalance.

Liver Disease

Patients with chronic liver disease often experience bone loss and are at high risk for fractures. It may be because a poorly functioning liver leads to vitamin D deficiency and reduced calcium levels, which in turn prompt the body to remove calcium from bone.

In addition, liver inflammation is often treated with corticosteroids, which as noted, inhibit osteoblasts and diminish new bone formation and can also interfere with vitamin D metabolism and absorption of calcium.

Cancer

Bone tumors themselves weaken the skeleton, but so do metastatic tumor cells from other malignancies such as breast, lung, and prostate cancer that often spread to the bones. Osteoporosis can also be a side effect of hormone-blocking therapies used to treat breast, uterine, ovarian, and prostate cancers. Other cancer-killing drugs may also harm bone density.

In addition, hormone-dependent cancers may require surgery to remove the ovaries in women and the testicles or prostate gland in men, thereby cutting off the supply of bone-building sex hormones.

Treatment for brain tumors may involve anti-seizure drugs and these can predispose to low bone density. Used over the long term, anticonvulsants such as phenytoin may reduce vitamin D levels in the blood and increase the risk of developing osteoporosis.

Other Diseases

Medications used to treat depression and gastrointestinal acid reflux disorder have been linked to low bone density and higher fracture risk. Anticoagulant blood thinners such as heparin and warfarin for patients with cardiovascular disease have also been associated with a higher risk of fracture. Weight loss from medications, or bariatric surgery, or lifestyle modifications (diet) will result in bone loss. Bones respond to weight bearing, which is lowered with reduced weight to carry.

Read previous installments in this series:

For Your Patients: Osteoporosis -- the 'Silent Thief'

For Your Patients: What to Know About Osteoporosis Diagnosis and Treatment

For Your Patients: Osteoporosis and Fractures

For Your Patients: Men Get Osteoporosis, Too

"Medical Journeys" is a set of clinical resources reviewed by physicians, meant for the medical team as well as the patients they serve. Each episode of this journey through a disease state contains both a physician guide and a downloadable/printable patient resource. "Medical Journeys" chart a path each step of the way for physicians and patients and provide continual resources and support, as the caregiver team navigates the course of a disease.