The short answer: calcium, vitamin D, protein, weight-bearing exercise, and a handful of supporting nutrients work together to keep your bones strong. But the details matter, because bones are living tissue that constantly breaks itself down and rebuilds, and what you eat and do each day directly shapes how well that process works.
How Your Bones Stay Strong
Bones aren’t static. Your body runs a continuous renovation cycle where specialized cells called osteoclasts dissolve old or damaged bone, and builder cells called osteoblasts move into those cleared spaces and deposit fresh, stronger tissue. This cycle runs automatically throughout your life, but the balance between breakdown and rebuilding shifts depending on your age, nutrition, and activity level.
You reach your peak bone mass by the end of your second decade of life, roughly your late teens to early twenties. Everything you do before that point builds your bone “bank account,” and everything after that point determines how quickly you withdraw from it. That doesn’t mean it’s too late if you’re past 20. The right combination of nutrients and exercise can slow bone loss significantly and even modestly improve bone density at any age.
Calcium: The Foundation
Calcium is the primary mineral your bones are made of, and your body can’t manufacture it. You have to get it from food or supplements. How much you need depends on your age and sex:
- Children 1–3 years: 700 mg per day
- Children 4–8 years: 1,000 mg
- Ages 9–18: 1,300 mg (the highest requirement, since bones are growing rapidly)
- Adults 19–50: 1,000 mg
- Women over 50: 1,200 mg
- Men over 70: 1,200 mg
The jump to 1,200 mg for women after 50 exists because bone loss accelerates after menopause. If you’re in that group, the extra 200 mg daily helps offset what hormonal changes take away.
Best Food Sources of Calcium
Dairy gets all the attention, but plenty of other foods deliver serious calcium. A half cup of tofu prepared with calcium sulfate contains 434 mg, nearly half a day’s requirement for most adults. Three ounces of canned sardines provide 325 mg. Among vegetables, cooked collard greens deliver 268 mg per cup, cooked spinach has 245 mg, turnip greens offer 197 mg, and cooked kale provides 177 mg. Bok choy comes in at 185 mg per cup.
Spreading your calcium across multiple meals improves absorption, since your body can only take in so much at once. A cup of greens at lunch and some tofu at dinner will serve you better than trying to hit your target in a single meal.
Vitamin D Makes Calcium Work
Your body can absorb calcium only if it has enough vitamin D. Without it, much of the calcium you eat passes through unused. The recommended daily intake is 600 IU for anyone ages 1 to 70 and 800 IU for adults over 70. Infants need 400 IU.
Sunlight triggers vitamin D production in your skin, but geography, skin tone, sunscreen use, and time spent indoors all reduce how much you actually make. Fatty fish, egg yolks, and fortified milk or orange juice help fill the gap. Many people, especially those living in northern climates or spending most of their day indoors, still fall short and benefit from a supplement.
Vitamin K: The Traffic Director
Vitamin K plays a less well-known but critical role. It activates proteins that pull calcium out of your bloodstream and deposit it into bone. One of these proteins, osteocalcin, essentially grabs calcium and delivers it to the bone matrix for incorporation into the hard mineral structure. Without enough vitamin K, this transfer process stalls, and calcium can end up lingering in your blood vessels instead of strengthening your skeleton.
Leafy greens like kale, spinach, and collard greens are rich in vitamin K, which means they do double duty: supplying both calcium and the nutrient that helps direct it where it needs to go.
Protein Supports the Bone Framework
About half of bone volume is protein, primarily collagen, which forms the flexible framework that calcium crystals attach to. A systematic review and meta-analysis commissioned by the National Osteoporosis Foundation found moderate evidence that higher protein intake has a small protective effect on bone mineral density in the lower spine compared to lower protein intake. The effect was modest (about a 0.5% net improvement) but consistent across studies.
You don’t need to eat enormous amounts of protein. Hitting the general recommendation of 0.8 to 1.0 grams per kilogram of body weight covers most adults. Older adults may benefit from slightly more, since both muscle and bone maintenance become less efficient with age.
Exercise That Builds Bone
Bones respond to mechanical stress by getting denser and stronger. The key is choosing activities that force your skeleton to bear load. Two categories matter most:
Weight-bearing aerobic exercise means any activity you do on your feet where your bones support your body weight. Walking, dancing, stair climbing, low-impact aerobics, elliptical training, and even gardening all count. These work directly on bones in your legs, hips, and lower spine to slow bone loss.
Strength training uses free weights, resistance bands, or your own body weight to stress bones and the muscles attached to them. It’s especially helpful for building the back muscles that support posture, and it directly stimulates bone density. Upper-back exercises are particularly valuable because the vertebrae in your spine are among the most vulnerable to osteoporosis-related fractures.
Flexibility exercises and balance training round out a bone-healthy routine. They won’t increase density on their own, but they reduce the risk of falls, which is how most osteoporosis-related fractures actually happen. Aim for a mix of these activities most days of the week.
What Hurts Your Bones
Some everyday habits quietly drain calcium from your body. Caffeine increases the amount of calcium you excrete through urine. Moderate coffee drinking (one to two cups a day) has only a slight effect on calcium balance, but heavy intake (more than about four cups daily) meaningfully increases calcium loss. Postmenopausal women are advised to keep caffeine to one to two servings per day.
High sodium intake also pushes calcium out through your kidneys. Processed foods, restaurant meals, and salty snacks are the biggest contributors for most people. Cutting back on sodium does more than help your blood pressure; it helps your bones hold on to the calcium you’ve worked to consume.
Smoking and excessive alcohol are two more well-established bone threats. Smoking interferes with the activity of bone-building cells, and heavy drinking disrupts the hormones and nutrients that regulate bone turnover.
Bone Density Screening
The U.S. Preventive Services Task Force recommends bone density screening for all women 65 and older. Postmenopausal women younger than 65 who have risk factors (small frame, family history, smoking, long-term steroid use, early menopause) should talk to their provider about earlier screening. The standard test is a DEXA scan, a quick, painless X-ray that measures mineral density at the hip and spine.
For men, there isn’t currently enough evidence to recommend routine screening, though men with known risk factors can still be assessed on an individual basis. These guidelines apply to adults 40 and older who haven’t already been diagnosed with osteoporosis or experienced a fracture from minor trauma.