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It’s one of the most common reasons for missed work and 50 percent of all working Americans suffer from it. No, we’re not talking about the flu or common cold– we’re talking low back pain.

According to the New England Journal of Medicine, 31 million Americans experience low back pain at any given time. Often times, back pain is related to aging. We may be used to thinking about superficial signs of aging-- like wrinkles and gray hairs-- but the inside of the body ages, too.

The spine is comprised of bones, called vertebral bodies, which stack on top of each other to form a column. This column serves as a support for the entire body. Between those bones are cushions called discs, which act as shock absorbers that prevent the bones from hitting each other when the body moves. Over time, these discs accumulate wear and tear. They dry up, get flattened and, occasionally, they bulge out to the sides. By the time we reach age 30, most of us will show some of these age-related signs of damage.

When scientists first noticed these changes, they named the condition “degenerative disc disease.” We now know that this isn’t actually a disease, it’s just a normal part of the aging process that happens to cause low back pain.

Currently, doctors and researchers don’t know what causes discs to start hurting or why disc pain affects certain people. They do know that certain activities put more stress on already painful discs. For example, sitting puts more pressure on the discs than lying down or standing does. The common motions of sitting, bending and twisting put a tremendous amount of pressure on the spine and are especially bad for people who already have wear and tear on the discs.

The other major cause of low back pain is wear-and-tear of the joints in the spine¬, or osteoarthritis. A joint is any area where one bone comes into contact with another bone. Over time, those bones can grind against each other and cause pain. The pain is usually worse when people stand and walk and eases when you sit down or lean forward. Osteoarthritis is the most common cause of disability in the U.S.

Another age-related discomfort is pain radiating from the back into the buttocks and legs. This occurs when inflammation from either a disc or a joint is irritating one of the nerves that travels from the spine down the leg. Since nerves carries sensation, pain can be felt on the nerve’s pathway in the body. The problem may be in the low back but can be felt in the leg.

Here are some of the biggest signs that your back pain is serious;

Constant pain that doesn't change as you move around
If you have pain that doesn’t change when you shift positions of your body (going from standing to sitting, for example), it may not be from wear and tear. Usually age-related causes of low back pain change with position. See your doctor when you have pain that’s constant and doesn’t change in severity throughout the day.

Difficulty moving your legs & changes in your bowel or bladder habits
If you have weakness in the legs or if you have problems with your bowel or bladder, see the doctor immediately. You want to make sure that there isn’t a tumor or cancer in the spine that’s irritating the bones and nerves. You also want to make sure that there’s no nerve damage from other causes.

Fever
People who have a fever with low back pain should visit a doctor to make sure it’s not being caused by an infection. Certain medical conditions, like diabetes, increase your risk for developing infections in the spine. Bacteria can cause abscesses, which are pockets of pus, that can lead to spinal cord injuries. Bacteria and viruses can also spread from the spine to the brain and spinal cord. They can lead to infections like meningitis, which can be deadly.

Even if you don’t have these warning signs, if you have consistent pain over six months, see your doctor and get a CT scan or MRI. These tests will show signs of aging, but will not point to the source of the pain. For example, if you are 60 or over, an MRI will likely show degenerative disc disease or osteoarthritis, but more importantly, will screen you for cancer, a tumor, bleeding, infection and broken bones.

Luckily, bodies are not like old beat-up cars. When you get a dent in your bumper, you’re pretty much stuck with it, but the human body is superior to all other man-made devices because it can heal itself. If you get a paper cut, it typically disappears within a couple days. In the same way, if you injure your spine, your body will repair the damage. You just need to give it the appropriate conditions to do so.

Rest is a good idea if you’re having one of your first episodes of low back pain. You can also try over-the-counter ointments, patches and medications to control the pain while your body is working on healing.

If the initial pain goes away but comes back regularly, seek out physical therapy or start an exercise regimen that helps stretch and strengthen the muscles of the back. Strengthening the muscles can take some of the load off the discs and joints.

Medications, procedures and surgery can also be helpful in cases of chronic low back pain. Cognitive behavioral therapy, chiropractic, alternative and complementary strategies can also be useful.

There is no way to completely prevent low back pain, but there is some evidence that diet and exercise can help.

Scientists have discovered that high blood pressure and high cholesterol affect the arteries carrying blood and other nutrients to the discs of the spine. When those arteries get damaged, it becomes harder for the discs to heal and the cycle of low back pain continues.

Eating heart-healthy foods rich in omega-3 fatty acids, like salmon and tuna fish, and having a diet rich in whole grains, beans and nuts can improve blood flow in your body. These foods decrease your risk of high blood pressure and high cholesterol, which will improve the blood flow to your spine, so your body can send nutrients to injured areas and heal the damage.

We can’t stop the spine from aging but we can do things to keep it healthy. Every medical treatment—whether it’s bed rest, physical therapy, medications, procedures or surgery—is a “bridge” that buys the body time to heal itself.

Devi Nampiaparampil, M.D. (“Doctor Devi”) is an Assistant Professor in the Department of Rehabilitation Medicine at the NYU School of Medicine.  Follow her at @devichechi. www.doctordevi.com