What are the causes and risk factors of osteoporosis?

Cause of osteoporosis

Bones are naturally renewing themselves on a constant basis. New bone is made when old bone breaks down. In younger people (those below the age of 35), bones are made faster than they are broken down, which increases bone mass.

The likelihood of developing osteoporosis depends partly on how much bone mass has been attained during youth and on other risk factors that may be present in an individual (see risk factors below). When peak bone mass (the amount of bone present upon skeletal maturation) is higher, a person will have more bone in their ‘bone bank’, reducing their chances of developing osteoporosis at a later age.  

Risk factors for osteoporosis

There are a number of risk factors that have been identified that may increase the likelihood of developing osteoporosis. These are mentioned below:

Unchangeable risks

Risk factors that cannot be controlled include:

• Gender⁴ – Women have a much higher rate of developing osteoporosis and are four times more likely to suffer from osteoporosis than men¹. There are a number of reasons why women have a higher risk factor than men, some of these are that:
  • Women tend to have naturally thinner and smaller bones than men.
  • Oestrogen, a vital hormone in the protection of bones, decreases significantly after a woman reaches menopause, which can result in bone loss.
• Age – The older one is, the higher the risk of osteoporosis.
• Race⁴ – Asian and Caucasian people are at higher risk of developing osteoporosis.
• Family history – Having a parent or sibling with osteoporosis, may increase one’s chances of developing the condition. Particularly if a parent has suffered an osteoporosis-related hip fracture.
• Small and thin body frame – Women and men who have smaller, thinner body frames have a higher risk osteoporosis due to the fact that they often have lower bone mass to draw from as they age.
• Inherited disorders of the connective tissue – These include homocystinuria, osteoporosis-pseudoglioma syndrome, osteogenesis imperfecta and skin disorders such as Ehlers-Danlos syndrome and Marfan syndrome. These are all causes of hereditary secondary osteoporosis and are all treated differently.

Hormone levels

People who have issues with their hormone levels, such as having too little or too much of certain hormones, have a higher risk of developing osteoporosis. These include issues with the following hormonal levels:

• Sex hormones – If sex hormones (testosterone and oestrogen in particular) are abnormally low (this is known as hypogonadism), this tends to result in a weakening of the bones as these hormones play a role in the remodelling, maintenance and growth of bones during each stage of life. When oestrogen levels are reduced in women during menopause or due to the removal of both ovaries, the risk of developing osteoporosis is increased.
  
  Men naturally experience a gradual decrease in testosterone levels as they age and while these don’t drop significantly like women’s oestrogen levels do at menopause, certain medications and treatments may affect them. Both treatments for prostate cancer in men and various treatments for breast cancer in women reduce testosterone and oestrogen levels respectively and may accelerate bone loss. Chemotherapy can also cause early menopause in women and disrupt the hormones.
  
  Another disorder that results from depleted hormone levels in women is known as Amenorrhea. This condition that describes the loss of menstrual periods for more than six months as a result of eating disorders, significant weight loss or intense exercise and training. Women in these situations will often have an unhealthy body weight, this can lead to a depletion on their oestrogen levels. When these hormones are lacking, bone density may take a toll from the disruption of hormones and their delicate balance.
• Thyroid issues – If the body produces too much of the thyroid hormone thyroxine or too little thyroid-stimulating hormone (TSH) over an extended period, this may result in bone loss. This often occurs when the thyroid is overactive (hyperthyroidism) or in cases where underactive thyroid (hypothyroidism) treatment leads to elevated thyroid hormone levels. 

• Other glandular issues – Hyperparathyroidism refers to a condition wherein an excessive amount of parathyroid hormone is produced by the parathyroid gland, this is a small gland that is usually located behind the thyroid gland. The parathyroid hormone will normally maintain the levels of calcium in the blood which is done, in part, by removing some of the calcium from bones. If this condition is left untreated then excessive amounts of parathyroid hormone may lead to large amounts of calcium being removed from the bones, resulting in osteoporosis.

Dietary risk factors

Osteoporosis is more likely to affect people with the below factors or conditions:

• Low intake of calcium – When levels of calcium have been lacking for most of one’s life, osteoporosis may occur. A low intake of calcium contributes to bone density depletion, an increased risk of fractures and early bone loss.
• Vitamin D – If vitamin D levels are low, the body is unable to absorb the right amount of calcium from the food consumed to prevent the development of osteoporosis. A vitamin D deficiency may result from insufficient exposure to sunlight, a lack of intestinal absorption which is often seen in primary biliary cirrhosis and celiac sprue, or a lack of the vitamin in one’s diet.

**My Med Memo – Calcium is a vital mineral needed for everyday life as it works together with vitamin D to protect, maintain and build the bones. Vitamin D is important in helping the body to absorb calcium effectively.

• Eating disorders – By restricting one’s food intake and being severely underweight, which is often the case in those suffering from anorexia or bulimia, bones are weakened and sufferers risk the development of osteoporosis.
• Gastrointestinal surgery – Undergoing surgery to remove a part of the intestine or to shrink the size of one’s stomach in order to lose weight, limits the surface area able to absorb vital nutrients like calcium, from the diet.

Steroids and certain medications

Using injected or oral corticosteroids such as cortisone or prednisone, for an extended period of time may interfere with the bone’s ability to rebuild itself. Osteoporosis has been associated with a number of medications and treatments that are used to prevent or treat the following conditions:

• Gastric reflux
• Cancer
• Seizures
• Transplant rejection

Medical conditions

The risk of developing osteoporosis is higher if one has certain medical conditions, some of which include:

Gastrointestinal and digestive disorders:

• IBD (Inflammatory bowel disease)
• Celiac disease
• Surgery for weight loss

Cancer:

• Prostate cancer
• Breast cancer

Autoimmune disorders:

• Lupus
• RA (rheumatoid arthritis)
• MS (multiple sclerosis)
• Ankylosing spondylitis – This is an inflammatory form of arthritis that affects the large joints and spine

Medical procedures:

• Gastrointestinal bypass procedures
• Gastrectomy

Blood/hematologic disorders:

• Multiple myeloma
• Leukaemia and lymphoma
• Sickle cell disease

Nervous system/neurological disorders:

• Multiple sclerosis (MS)
• Stroke
• Spinal cord injuries
• Parkinson’s disease

Hormonal/Endocrine disorders:

• Hyperparathyroidism
• Hyperthyroidism
• Thyrotoxicosis
• Diabetes
• Low levels of sex hormones oestrogen and testosterone in men
• Cushing’s syndrome
• Irregular periods
• Premature menopause

Bone marrow and blood disorders:

• Thalassemia – This is a blood conditions that results in low amounts of the oxygen-carrying protein known as haemoglobin

Other disorders and conditions:

• Amenorrhea
• COPD (Chronic obstructive pulmonary disease) – This includes emphysema
• Chronic kidney disease
• AIDS/HIV
• Weight loss
• Organ transplants
• Liver disease – This includes biliary cirrhosis
• Polio – This includes post-polio syndrome
• Poor diet – This also include malnutrition
• Scoliosis

Lifestyle risk factors

There are a few bad habits that may increase the risk of developing osteoporosis, some examples include:

• Use of tobacco products – The role that tobacco products have to play is not clearly understood, however, what is known is that these products and the use of them contributes to the weakening of bones.
• Excessive consumption of alcohol – Consuming more than four drinks per day for men or three per day for women, may increase the risk of osteoporosis. Alcohol is able to affect the levels of calcium in the body. If you consume too much alcohol, then your stomach may be unable to absorb calcium sufficiently. Alcohol also interferes in your pancreas and its ability to absorb vitamin D and calcium. On top of this, alcohol will also affect your liver, which is a vital organ for activating the vitamin D in your body.
• Sedentary lifestyle – Those who spend the majority of their time sitting have a higher risk of developing osteoporosis in comparison to those who live a more active lifestyle. Any activities or exercises that promote good posture and balance are considered beneficial for the bones. Exercises such as running, jumping, walking and weightlifting have been identified as particularly good for preventing osteoporosis.

 

^References

^{1. University of Rochester. Osteoporosis. Available: https://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=85&ContentID=P00932 [Accessed 31.08.2017]}

^{4. Harvard Health Publications. October 2012. Osteoporosis. Available: https://www.health.harvard.edu/pain/osteoporosis [Accessed 31.08.2017]}