Many things can decrease bone density, from hormonal shifts and nutritional gaps to medications, lifestyle habits, and certain medical conditions. Your skeleton is constantly rebuilding itself through a process where old bone is broken down and new bone takes its place. When that cycle tips out of balance, with more bone removed than replaced, density drops and fracture risk climbs.
How Bone Loss Actually Happens
Your body has two types of bone cells doing opposite jobs. One type breaks down old or damaged bone, and the other fills in the gaps with fresh bone tissue. In healthy adults, these two processes stay roughly in sync, so each repair cycle ends with the cavity fully refilled. In conditions like osteoporosis, the bone-building cells can’t keep up. Each cycle leaves a small deficit, and over months and years, those small deficits add up to measurably weaker bones.
Almost every factor on this list works by tilting that balance: either speeding up breakdown, slowing down formation, or both at once.
Hormonal Changes, Especially After Menopause
Estrogen acts as a brake on bone breakdown. When estrogen levels drop sharply during menopause, that brake releases and the breakdown cells become overactive. Women typically lose 1 to 5% of their bone mass per year during the first five to seven years after menopause, a pace that far outstrips normal age-related loss. This is the single biggest driver of osteoporosis in women.
Low testosterone plays a similar, though less dramatic, role in men. And in both sexes, an overactive thyroid gland speeds up the entire bone remodeling cycle. The breakdown phase accelerates more than the rebuilding phase, creating an imbalance that leads to rapid bone loss if the thyroid condition goes untreated.
Vitamin D Deficiency and Calcium Shortfalls
Vitamin D controls how much calcium your gut absorbs from food. When vitamin D levels are low, less calcium makes it into your bloodstream, and your body responds by releasing parathyroid hormone. This hormone’s job is to keep blood calcium stable at all costs, and the fastest way it does that is by pulling calcium out of your bones. The result: your blood calcium stays normal, but your skeleton pays the price through increased bone turnover and gradual loss.
Calcium intake matters too, but not in isolation. Without adequate vitamin D, even a calcium-rich diet won’t fully protect your bones because the mineral simply isn’t absorbed efficiently.
High Salt Intake
Salt forces your kidneys to excrete more calcium in urine. On average, for every 100 millimoles of sodium you consume (roughly the amount in a high-salt Western diet), you lose about 1 millimole of calcium through your urine. That may sound small, but over years of consistently high sodium intake, the cumulative calcium drain chips away at bone reserves. People with high blood pressure lose even more calcium per unit of sodium than those with normal blood pressure, making them especially vulnerable.
Corticosteroids and Other Medications
Oral corticosteroids (like prednisone, often prescribed for autoimmune conditions, asthma, or inflammatory diseases) are one of the most well-documented medication causes of bone loss. Bone density drops rapidly in the first three to six months of use, and fracture risk rises in a dose-dependent way. Taking 5 mg or more of prednisone daily for three months or longer is enough to meaningfully increase risk. At doses of 7.5 mg per day or higher, the probability of a major fracture jumps by at least 15%. In the first six months of corticosteroid therapy, the annual rate of spinal fractures is around 5%.
Acid-suppressing medications known as proton pump inhibitors also carry risk. A meta-analysis of 11 studies found that older adults on these drugs had a 41% higher fracture risk compared to non-users. The likely mechanism is reduced calcium absorption in a less acidic stomach environment. These medications are widely prescribed and often continued for years, which makes the cumulative effect significant.
Smoking
Nicotine directly slows the production of bone-building cells, so less new bone is formed during each remodeling cycle. Smoking also decreases calcium absorption from your diet, compounding the problem. The effect is dose-related: the more you smoke and the longer you’ve smoked, the greater the impact on bone density. Quitting doesn’t instantly reverse the damage, but it does allow bone-building activity to gradually recover.
Heavy Alcohol Use
Alcohol disrupts bone health through several overlapping pathways. In the short term, even a single episode of heavy drinking (roughly five or more drinks in a few hours) causes parathyroid hormone levels to drop sharply, then rebound above normal. That rebound triggers a burst of bone breakdown. Over the long term, chronic heavy drinking is associated with persistently low blood calcium levels, poor nutritional absorption, and impaired bone-building cell function.
Moderate drinking (one drink per day for women, two for men) has not been consistently linked to bone loss, and some studies suggest very light drinking may even be neutral or slightly protective. The harm is clearly concentrated at higher intake levels.
Prolonged Sitting and Inactivity
Bone responds to mechanical loading. When you stand, walk, or lift something heavy, the stress on your skeleton signals bone-building cells to stay active. Remove that stimulus, and bone formation slows. Research on older women found that spending long periods sitting without interruption, particularly bouts longer than 20 to 60 minutes, was associated with measurable declines in spinal bone density over time. This association held even after accounting for how much exercise participants did elsewhere in their day.
That’s a key finding: you can’t fully offset hours of unbroken sitting with a single exercise session. Breaking up sedentary time every 20 minutes or so appears to matter independently for bone health, especially for older women who are already at higher risk for osteoporosis.
Factors That Compound Each Other
In practice, bone loss rarely comes from a single cause. A postmenopausal woman who takes corticosteroids, has low vitamin D, and sits most of the day faces a much steeper decline than any one of those factors would produce alone. Each remodeling cycle that ends with a deficit stacks on the last one, and the combination of accelerated breakdown and slowed formation can shrink bone density at rates several times the normal age-related pace.
The most actionable items on this list, adequate vitamin D and calcium, reduced sodium, regular weight-bearing movement, quitting smoking, and limiting alcohol, are also the ones within your direct control. Medication-related bone loss is harder to avoid when the drug treats a serious condition, but awareness of the risk allows for monitoring and protective steps before fractures occur.