Smoking is a risk factor for osteoporosis and bone fractures. We have all heard about the relationships between smoking and asthma, bronchitis, chronic obstructive pulmonary disease, lung cancer, and heart disease. But smoking and even second-hand smoke increase the risk of osteoporosis. Smoking cessation reverses that risk.
53 million people in the United States either are at risk for or already have osteoporosis. Smoking or exposure to tobacco smoke can be the "last straw" for people who have any or many of a number of other risk factors:
- Family history of osteoporosis.
- Small stature, "small bones."
- In women, late onset of first period or early menopause.
- Low calcium intake.
- Excessive alcohol intake.
- Lack of physical activity.
- Use of steroid medications for asthma or autoimmune disease.
How much greater is the risk of osteoporosis for smokers?
One of out of eight women who don't smoke will suffer a hip fracture by age 85. One out of every five women who smoke will have a broken hip by the same age.
Smoking increases the lifetime risk of a spine fracture by 13 percent in women and by 32 percent in men. Smoking increases the lifetime risk of a hip fracture by 31 percent in women and by 40 percent in men. Of the male smokers who have hip fractures, over one-third will die within two years of their broken hip.
How does smoking destroy bone?
Smoking affects bone growth indirectly through increasing stress hormones, interfering with sex hormones, interfering with appetite, lowering body weight (reducing the stimulation of new bone growth), interfering with the interaction of parathyroid hormone and vitamin D, and depleting antioxidants that protect bone. Smoking affects bone growth directly by interrupting a genetic pathway known as RANKL-RANK-OPG that is essential for developing new bone. Let's take a closer look at some of the effects of smoking on bone:
- Smoking reduces appetite. When you eat less, you eventually weigh less. When you weigh less, the muscles put less of a load on the bones, so they are not activated to remodel themselves by breaking down old bone and building up new bone. When you eat less, you put on less fat. That's not always a good thing, because fat cells generate estrogen (even in men) to stimulate the production of bone.
- Smoking elevates liver enzymes. Toxic effects in the liver interfere with its ability to "activate" vitamin D. They also reduce the production of parathyroid hormone. Lowering parathyroid hormone reduces the ability of bones to absorb calcium and vitamin D.
- Smoking elevates bloodstream concentrations of the stress hormone cortisol. When cortisol levels go up, absorption of calcium from food goes down. Stress reduces the amount of calcium available to bones.
- In women, smoking accelerates menopause. Women who smoke will reach menopause around two years before non-smokers. Estrogen production goes down, and less estrogen is available to stimulate production of new bone.
- In men, over the long term, smoking reduces testosterone production. (There actually can be short-term increases in testosterone production after smoking men, but the overall long-term effect is lower testosterone.) There is less testosterone for a man's fat cells to convert into bone-stimulating estrogen, and fewer fat cells to convert it. In those fat cells that still can produce estrogen, the aromatase enzyme needed for the process is partially disabled by chemicals found in smoke.
- In both men and women, smoking increases the production of sex hormone binding globulin, also known as SHBG. This protein binds estrogen and keeps it from reaching bone.
- Tobacco smoke (including second-hand smoke) is filled with toxic free radicals. These free radicals deplete antioxidants needed for energy production in bone-building cells.
- Nicotine interferes with angiogenesis, the formation of new blood vessels to bring nutrients and oxygen to growing bone.
- Low levels of nicotine actually stimulate the osteoblasts, cells that build new bone, but high levels of nicotine kill them. This includes nicotine from nicotine patches.
- Polycyclic aryl hydrocarbon compounds from tobacco enter circulation and kill bone.
- Smokers have reduced muscle mass. With less muscle, falls are more likely. More falls, more fractured bones.
It's not easy to stop smoking, but all of the toxic effects of smoking on bones can be reversed if you simply stop smoking or get out of the path of second-hand smoke. That does not mean that the benefits of smoking cessation are immediate. There is an elevated risk of fractures for 10 years after you stop smoking. Ten years after you quit and after, the effects of smoking on your bones are minimal and your lifetime risk of fracture is greatly reduced.