Bones are far more than a rigid framework that holds your body together. They are living tissue that constantly regenerates, stores minerals, and is even involved in blood production. An average adult has about 206 bones, which together make up only about 15 percent of body weight, but possess remarkable strength – healthy bone can support a weight of over 1,700 kilograms per square centimeter, similar to granite.

Bones are alive

Many people imagine bones as inert material, comparable to the wooden frame of a house. In reality, bones are highly active tissue with a fascinating metabolism. Two cell types play the main roles: osteoblasts build new bone, while osteoclasts break down old bone. This constant remodeling, known as bone remodeling, ensures that the skeleton adapts to stress and that microscopic damage is repaired. In a healthy young adult, bone formation and resorption are in balance. Approximately every ten years, the entire skeleton is completely renewed. However, with increasing age, especially after menopause in women, this balance shifts in favor of resorption – the bone loses mass and stability.

Why bone health is important

The importance of strong bones often only becomes clear when they are weakened. Osteoporosis, the pathological loss of bone mass, affects approximately six million people in Germany, about 80 percent of whom are women. The disease initially progresses without symptoms – the bones become porous and brittle without being noticed. Only when a fracture occurs, often from a seemingly harmless fall or even spontaneously, does osteoporosis become apparent. Hip fractures are particularly feared, as they are associated with significant morbidity and even increased mortality in older people. Approximately 20 percent of people over 65 who suffer a hip fracture die within a year as a result. But vertebral fractures, which gradually lead to back pain and loss of height, also significantly impair quality of life. The good news: Much can be done for bone health through timely preventative care and a healthy lifestyle.

To understand and promote bone health, it helps to know the basics of bone metabolism. Bones consist of a mixture of organic and inorganic components that give them their unique properties: simultaneously hard and elastic, strong yet not brittle.

The composition of bone

Approximately 65 percent of bone mass consists of inorganic minerals, primarily calcium and phosphate in the form of hydroxyapatite crystals. These minerals give bone its hardness and compressive strength. The remaining 35 percent consists of organic material, mainly type I collagen, which forms an elastic network and gives bone tensile strength and some flexibility. This combination makes bone so resilient: the minerals withstand pressure, and the collagen prevents the bone from fracturing. If one of these elements is impaired—too few minerals in osteoporosis, defective collagen in osteogenesis imperfecta—bone stability is significantly compromised.

Bone metabolism

Bone remodeling follows a complex regulatory circuit influenced by hormones, mechanical stress, and nutrient supply. Parathyroid hormone, produced by the parathyroid glands, increases blood calcium levels by releasing calcium from bones and enhancing calcium absorption in the intestines and kidneys. Calcitonin, a hormone from the thyroid gland, has the opposite effect, promoting calcium incorporation into bone. Vitamin D, which is actually a hormone, is essential for calcium absorption from the intestines and influences both osteoblasts and osteoclasts. Estrogen has a strong bone-protective effect, which is why estrogen deficiency after menopause leads to accelerated bone loss. Mechanical stress also sends signals to bone cells: if a bone is regularly stressed, it becomes stronger; if it is not stressed, it is broken down—a principle that could be called "use it or lose it."

Bone density throughout life

Bone mass reaches its maximum, known as peak bone mass, between the ages of 25 and 30. The exact level of this peak depends on genetics, nutrition during childhood and adolescence, and physical activity. The higher the peak bone mass, the more bone reserves are available for later life. After the age of 30, a slow decline of approximately 0.5 to 1 percent per year begins. In women, this decline accelerates to 2 to 3 percent per year in the first few years after menopause, due to estrogen deficiency. Men are less affected but can also develop osteoporosis, especially if they have risk factors such as low testosterone or are undergoing cortisone therapy.

Osteoporosis is a systemic skeletal disease in which bone mass decreases and bone structure deteriorates, resulting in increased bone fragility. The disease is often referred to as a 'silent epidemic' because it often progresses without symptoms for a long time and only becomes clinically apparent through fractures.

Primary and secondary osteoporosis

Primary osteoporosis is the most common form and includes postmenopausal osteoporosis in women after menopause, as well as senile osteoporosis in older age in both sexes. These forms are caused by the natural aging process and hormonal changes. Secondary osteoporosis, on the other hand, results from other diseases or medications. Causes include long-term therapy with glucocorticoids such as cortisone, the most common drug-related cause, hyperthyroidism, hyperparathyroidism, chronic inflammatory bowel diseases with malabsorption, celiac disease, rheumatoid arthritis, diabetes mellitus, and chronic alcohol abuse.

Identify risk factors

Besides age and female sex, there are numerous other risk factors. Non-modifiable factors include genetic predisposition (a hip fracture in one's parents doubles the risk), small and slender build with low bone mass, and early menopause before the age of 45. Modifiable risk factors include calcium and vitamin D deficiency, lack of exercise, smoking (which lowers estrogen production and directly inhibits osteoblasts), excessive alcohol consumption, being underweight with a BMI below 20, a high tendency to fall, and certain medications. Knowledge of these risk factors enables targeted prevention.

Warning signs and diagnosis

Osteoporosis causes no symptoms in its early stages. Later, however, signs may appear: back pain, especially in the thoracic and lumbar spine, can indicate vertebral fractures. A loss of height of more than four centimeters results from vertebral collapse. A progressive rounding of the back, medically termed kyphosis and colloquially known as a "dowager's hump," is a typical sign of advanced vertebral osteoporosis. Fractures from minor trauma, known as fragility fractures, are often the first obvious sign. Diagnosis is made through a bone density measurement, specifically a DXA scan, which determines bone density in the lumbar spine and hip. The result is expressed as a T-score: values ​​above -1 are normal, -1 to -2.5 indicate osteopenia, a precursor to osteoporosis, and below -2.5 indicates osteoporosis.

Calcium is the most abundant mineral in the human body. An adult contains approximately one kilogram of it, and 99 percent of this is stored in bones and teeth. These calcium reserves not only ensure bone stability but also serve as a storage depot from which the body can mobilize calcium when needed for other vital functions – such as muscle function, nerve conduction, and blood clotting.

How much calcium do you need?

The German Nutrition Society recommends a daily calcium intake of 1000 milligrams for adults. For adolescents during their growth phase, the recommendation is 1200 milligrams, as it is for pregnant and breastfeeding women. Many experts also recommend 1200 milligrams daily for postmenopausal women and people with osteoporosis. However, the reality is often different: many people, especially women and older adults, consume less calcium than recommended. Dairy products are the main source of calcium in the German diet, and those who avoid or reduce their consumption must consciously pay attention to other calcium sources.

The best sources of calcium

Milk and dairy products are the richest sources of calcium in the Western diet. A glass of milk contains about 240 milligrams of calcium, a slice of cheese between 200 and 400 milligrams depending on the type, and a cup of yogurt about 180 milligrams. Hard cheeses like Parmesan are particularly rich in calcium. But calcium needs can also be met without dairy products: Green vegetables such as broccoli, kale, bok choy, and arugula contain readily available calcium. Sesame seeds and tahini are excellent sources. Almonds contain about 250 milligrams per 100 grams. Calcium-rich mineral water often provides 300 to 500 milligrams per liter. Calcium-fortified plant-based milk can be a good alternative if it is shaken well before pouring, as the calcium settles out. Fish with edible bones, such as canned sardines, is also a good source.

Optimize calcium absorption

Not all ingested calcium is absorbed by the body. Several factors influence absorption: Vitamin D is essential for calcium absorption in the intestines – in cases of vitamin D deficiency, even a high calcium intake cannot be adequately absorbed. Phytic acid in whole grain products and legumes, as well as oxalic acid in spinach, rhubarb, and beetroot, can inhibit calcium absorption, but this should not be overemphasized in a balanced diet. Caffeine and salt slightly increase calcium excretion via the kidneys. High phosphate levels, such as those found in cola drinks, can disrupt the calcium-phosphate balance. Alcohol inhibits calcium absorption and promotes its excretion.

Strictly speaking, vitamin D is not a vitamin, but a hormone that the body can produce itself – provided it receives enough sunlight. Without sufficient vitamin D, the body cannot effectively absorb calcium from food, even if enough is consumed. Therefore, vitamin D is at least as important for bone health as calcium itself.

Vitamin D and bones

Vitamin D's primary function for bone health is to promote calcium absorption in the small intestine. Without vitamin D, only about 10 to 15 percent of ingested calcium is absorbed; with sufficient vitamin D, this figure rises to 30 to 40 percent. A vitamin D deficiency lowers blood calcium levels, prompting the parathyroid glands to release parathyroid hormone, which mobilizes calcium from the bones. The result: long-term demineralization of the bones. Severe, prolonged vitamin D deficiency leads to rickets in children, characterized by deformed bones, and to osteomalacia in adults, with soft, painful bones. Even moderate deficiencies contribute to osteoporosis.

Vitamin D supply in Germany

Vitamin D can be produced in the skin when it is exposed to UVB radiation. In Germany, however, this is only possible from about April to September, and even then only if one spends time outdoors regularly and exposes arms and legs to the sun without covering them. During the winter months, the sun is too low in the sky, and the UVB radiation is insufficient for vitamin D synthesis. As a result, about 60 percent of the German population does not have optimal vitamin D levels; this figure is even higher in winter. Older people are particularly at risk, as vitamin D synthesis in the skin decreases with age, and many spend less time outdoors.

Sources and Supplementation

Natural food sources of vitamin D are limited: Fatty fish such as salmon, herring, and mackerel are the best source. Liver, egg yolks, and mushrooms, especially if they have been UV-irradiated, also contain some vitamin D. However, these amounts are usually insufficient to meet daily requirements. Supplementation is therefore advisable for many people, especially during the winter months, for older adults, for people who spend little time outdoors, and in cases of diagnosed deficiency. The usual recommendation is 800 to 1000 IU daily; higher doses may be necessary in cases of diagnosed deficiency. The optimal blood level is between 40 and 60 ng/ml. A blood test can provide clarity about your individual vitamin D status.

Calcium and vitamin D are the stars of bone nutrition, but they are not the only relevant nutrients. An orchestra of vitamins and minerals works together to maintain bone health. A deficiency in any of these nutrients can impair bone health, even if calcium and vitamin D are present in sufficient quantities.

Vitamin K2 – The underestimated helper

Vitamin K, especially vitamin K2, plays a crucial role in bone metabolism. It activates osteocalcin, a protein that incorporates calcium into the bone matrix. Without sufficient vitamin K, ingested calcium cannot be effectively stored in the bones and could instead be deposited in blood vessels. Good sources of vitamin K2 include fermented foods such as natto, a Japanese soy product particularly rich in K2, as well as certain cheeses, egg yolks, and grass-fed animal products. Vitamin K1 is abundant in green leafy vegetables and is partially converted to K2 in the body. K2 supplementation may be beneficial for individuals with osteoporosis or at increased risk.

Magnesium – Essential for bone metabolism

Approximately 60 percent of the body's magnesium is stored in the bones. Magnesium influences both bone formation and the effects of vitamin D and parathyroid hormone. A magnesium deficiency can impair bone mineralization. Good sources of magnesium include nuts, seeds, whole grains, legumes, and green vegetables. Mineral water can also contribute to magnesium intake. The recommended daily intake is approximately 350 to 400 milligrams for adults.

Other important nutrients

Phosphorus is the second most important mineral in bones after calcium. A deficiency is rare in the Western diet; rather, an excess from cola drinks and processed foods is a more common problem, as it can disrupt the calcium-phosphate balance. Zinc is involved in over 300 enzyme reactions, including those in bone metabolism. Good sources include meat, seafood, nuts, and seeds. Manganese, copper, and boron are trace elements required in small amounts for bone health and are usually adequately ingested through a varied diet. Protein is important for the collagen matrix of bone. Both too little and excessive protein can impair bone health—a moderate, adequate protein intake is optimal. Vitamin C is essential for collagen synthesis and thus for the organic matrix of bone. A severe deficiency leads to scurvy with bone changes, but even suboptimal intake can impair bone health.

Bones respond to mechanical stress by adapting. If a bone is regularly stressed, it responds by strengthening – a principle known as Wolff's Law. If it is not stressed, it deteriorates. Astronauts lose significant bone mass during their time in weightlessness, and bedridden individuals experience rapid bone loss. Movement is therefore one of the most effective levers for bone health.

What kind of stress stimulates the bones?

Not every movement is equally effective for bones. The strongest stimuli come from weight-bearing and impact activities. Strength training is particularly effective because it exerts direct mechanical stress on the bones. Studies show that regular strength training can increase bone density or at least slow down bone loss, even in postmenopausal women. Weight-bearing endurance activities such as walking, jogging, and dancing stress the bones through body weight. Jumping and impact activities, such as skipping rope, basketball, or volleyball, send particularly strong signals to bone cells. Balance and coordination exercises are important for fall prevention, even if they stimulate the bones less directly. Swimming and cycling are excellent for the heart and circulatory system, but less effective for bones because they support body weight.

Practical recommendations

For optimal bone health, a combination of strength training two to three times a week is recommended, targeting all major muscle groups. The training should be progressive, meaning you should use increasing weights to provide continuous stimulation. Weight-bearing activities such as brisk walking, stair climbing, or dancing should be performed most days of the week. Balance exercises reduce the risk of falls, which is especially important as we age. The intensity of the training should be tailored to your individual fitness level. For people who already have osteoporosis, medical advice is essential to consider the fracture risk associated with certain exercises. However, even with osteoporosis, exercise is possible and important – it simply needs to be adapted.

The earlier, the better – but never too late

Bones respond most strongly to exercise stimuli during youth. Children and adolescents who are active and participate in sports develop a higher peak bone mass, which benefits them throughout their lives. But exercise is also effective in middle and old age: it can slow age-related bone loss, maintain muscle strength, and reduce the risk of falls. It's never too late to start exercising.

Besides diet and exercise, other lifestyle factors influence bone health. Some of these factors are clearly harmful, while others are underestimated. Understanding these connections makes it possible to make targeted changes.

Smoking – poison for the bones

Smoking is one of the most significant modifiable risk factors for osteoporosis. Its harmful effects are manifold: nicotine directly inhibits osteoblasts, the bone-building cells. Smoking lowers estrogen levels in women, which reduces bone protection. It impairs blood flow to bone tissue and affects calcium absorption. On average, female smokers reach menopause two years earlier than non-smokers, meaning that accelerated bone loss begins sooner. The risk of fractures is significantly increased in smokers. Quitting smoking is worthwhile at any age – while bones recover slowly, the progressive damage is halted.

Alcohol – The dose makes the poison

Moderate alcohol consumption, meaning one to two glasses for men and one glass for women per day, does not appear to significantly impair bone health and, according to some studies, may even have a slightly protective effect. Excessive alcohol consumption, on the other hand, is clearly harmful: it inhibits osteoblasts, disrupts calcium absorption, impairs the liver, which is important for vitamin D activation, and increases the risk of falls and fractures. Chronic alcohol abuse is a recognized risk factor for secondary osteoporosis.

Body weight and bone health

Being underweight is a risk factor for osteoporosis. At low body weight, the mechanical stress on the bones is lower, and the protective estrogen production in adipose tissue is lacking after menopause. Eating disorders such as anorexia lead to severe osteoporosis, often at a young age. On the other hand, while being overweight offers some protection against osteoporosis due to the higher mechanical stress and estrogen production in adipose tissue, significant overweight increases the risk of other health problems. A normal to slightly elevated body weight appears to be most beneficial for bone health.

Medications and bones

Certain medications can impair bone health. Glucocorticoids such as cortisone are the most significant, as the risk of fractures increases after just three months of therapy. Proton pump inhibitors used to suppress acidity can reduce calcium absorption with long-term use. Certain antiepileptic drugs affect vitamin D metabolism. Aromatase inhibitors used to treat breast cancer lower estrogen levels and accelerate bone loss. Bone health should be monitored and preventive treatment considered when taking these medications long-term.

Bone density measurement is the most important tool for diagnosing osteoporosis and assessing the risk of fractures. Since osteoporosis often remains asymptomatic for a long time, only a measurement can reveal the true condition of the bones. But who should get tested, and what do the results indicate?

The DXA measurement

The gold standard for bone density measurement is DXA, also known as DEXA, which stands for dual-energy X-ray absorptiometry. In this method, the lumbar spine and hip are scanned with two X-ray beams of different energies. The radiation exposure is very low, comparable to a fraction of that of a normal X-ray. The measurement takes about ten to twenty minutes and is painless. The result is expressed as a T-score, which indicates how much the bone density deviates from the average of healthy young adults. A T-score of 0 means average bone density, while negative values ​​indicate lower density. A T-score up to -1 is normal, -1 to -2.5 indicates osteopenia, a precursor to osteoporosis, and below -2.5, by definition, osteoporosis is present.

Who should have a bone density scan?

A bone density scan is recommended for women aged 65 and older and men aged 70 and older, as the risk of osteoporosis increases significantly from this age. For younger people with risk factors, an earlier scan is advisable: for women after early menopause before the age of 45, for those undergoing long-term cortisone therapy, for those with certain conditions such as rheumatoid arthritis, hyperthyroidism, or chronic inflammatory bowel disease, for those with a family history of osteoporosis or hip fractures, for those with previous fragility fractures, for those who are underweight, and for those who smoke heavily and consume excessive amounts of alcohol. Health insurance companies typically only cover the cost of the scan if there is a specific suspicion of osteoporosis or after a fracture; otherwise, it is a self-pay service.

Further examination options

The at-home osteotest can provide an initial assessment, although it does not completely replace a DXA scan. It can help determine whether further diagnostic testing is advisable. Laboratory tests can assess bone metabolism: blood calcium and phosphate levels, vitamin D, parathyroid hormone, as well as bone turnover markers such as osteocalcin and alkaline phosphatase provide information about bone metabolism and possible causes of bone loss.

Bone health isn't just a concern for older people. The foundation is laid in youth, when maximum bone mass is built. But even at any later age, there's a lot that can be done to strengthen bones and prevent fractures.

Key findings summarized

Bones are living tissue that responds to stress and nutrient supply. Maximum bone mass is built up until around the age of thirty, after which a slow decline begins, accelerating in women after menopause. Osteoporosis is a common disease that often remains asymptomatic for a long time and only becomes apparent through fractures. Approximately six million people in Germany are affected. Calcium and vitamin D are the most important nutrients for bones. The recommended daily calcium intake is 1000 to 1200 milligrams, and vitamin D should be supplemented for most people, especially during the winter months. Other nutrients such as vitamin K2, magnesium, and protein are also important. Exercise is one of the strongest stimuli for bone health. Strength training and weight-bearing activities are particularly effective. Balance training reduces the risk of falls. Smoking, excessive alcohol consumption, and certain medications damage bones.

What you can do specifically

For nutrition: Include calcium-rich foods daily, whether through dairy products, green vegetables, nuts, or fortified foods. Know your vitamin D levels and supplement if necessary, especially in winter. Ensure an overall balanced diet that provides all the nutrients needed for bone health. For exercise: Perform regular strength training, including bodyweight exercises. Incorporate weight-bearing activities into your daily routine, such as taking the stairs instead of the elevator. Practice balance exercises, especially as you get older. Optimize your lifestyle: Quit smoking, if applicable. Consume alcohol only in moderation. Aim for a healthy weight. Minimize the risk of falls in your home.

Prevention and early detection

A bone density measurement is worthwhile for those with risk factors or from a certain age. It can detect early-stage osteoporosis, when preventive measures can still be highly effective. A self-test can provide initial guidance and help decide whether further diagnostic testing is advisable. Strong bones are not a given, but achievable with the right lifestyle. Investing in bone health pays off – through mobility, independence, and quality of life well into old age.