Osteoporosis diet: what to eat to support bone health

What is osteoporosis, and why does it increase fracture risk?

Osteoporosis is a condition in which bones lose mineral density and their internal structure becomes more fragile. This means they can break after a minor knock or an everyday movement that would not previously have caused harm.

A doctor diagnoses it with a bone density scan. This measures bone density at the spine and hip and compares it with that of healthy young adults using a measure called the T-score. According to Spanish osteoporosis guidelines, a T-score below −2.5 indicates osteoporosis [1]. A score between −1 and −2.5 indicates osteopenia, a lesser loss of bone density.

It does not cause pain as it develops. Many people first discover it when they break a wrist after putting out a hand during a fall, or have a vertebral fracture while bending down to pick something up.

Bone loss accelerates in women after menopause as oestrogen levels fall. It also affects men, particularly in later life. Bones and muscles deteriorate together if they do not get the right stimulation.

How much calcium do you need each day, and how can food provide it?

For people with osteoporosis, Spanish guidelines recommend 1,000 to 1,200 mg of calcium a day [1]. For the general population, the reference intake is slightly lower: 950 mg a day from age 25, and 1,000 mg between ages 18 and 24 [2]. For people aged 50 and over, another European guideline puts needs at 800 to 1,000 mg and prefers calcium to come from food [3].

You can meet your needs through food if you plan your day.

• Dairy products. A glass of milk provides about 300 mg of calcium, a plain yoghurt about 150 mg, and 40 g of semi-hard or hard cheese 300 to 400 mg. You can have up to three servings a day, preferably plain and unsweetened. Two or three servings can provide more than half your target.
• Fish eaten with their bones. A small tin of sardines, including their soft bones, provides 300 to 350 mg.
• Plant sources. Ground sesame seeds or tahini, almonds, white beans, chickpeas and tofu set with calcium salts can help make up the rest.
• If you do not eat dairy. Choose a calcium-fortified soya drink, or another plant drink with at least 3% protein. Check the label. Bear in mind that soya is an allergen.

Not all calcium in vegetables is absorbed equally well. Calcium from broccoli, kale and cabbage is well absorbed. Spinach and Swiss chard, by contrast, contain oxalates, substances that bind almost all their calcium and prevent the gut from absorbing it. You can still enjoy them for the other nutrients they provide, but do not count them as calcium sources.

What does vitamin D do, and where can you get it?

Vitamin D helps the gut absorb calcium and keeps blood calcium levels in balance. For adults, the reference intake is 15 micrograms a day (600 international units), calculated for when the skin produces very little through sunlight [4].

For people with osteoporosis, Spanish guidelines advise keeping blood 25-hydroxyvitamin D above 20–25 ng/ml, and preferably above 30 ng/ml [1]. This is the marker measured in a blood test. To achieve this, they propose intakes of 800 to 1,200 international units a day [1]. Another European guideline gives 800 units a day as a reference from age 50 [3].

Food provides little vitamin D. Only some oily fish, such as salmon, mackerel and sardines, contain appreciable amounts, while egg yolk and fortified dairy products provide smaller amounts. Most is made in the skin through sunlight. Skin becomes less efficient at making it with age, and winter sunlight is not enough. That is why doctors so often check vitamin D levels.

Why do protein and strength exercise matter so much for bones?

We often picture bone as a block of minerals. Yet nearly a third of its mass is a flexible network of proteins, mainly collagen. Without enough protein, bone loses support and the muscles that protect it weaken.

For older adults, the European clinical nutrition guideline for geriatrics recommends at least 1 g of protein per kilogram of body weight a day [5]. A common reference is 1 to 1.2 g per kilogram; people who train may need more. For osteoporosis, the range is 1 to 1.5 g per kilogram [1]. For someone weighing 65 kg, that is 65 to 97 g a day, spread across main meals. If you have kidney disease, your nephrologist should set the amount.

Exercise helps stimulate bone and muscle formation alongside adequate protein. Strength exercise and walking for at least 30 minutes a day are basic measures for osteoporosis [1]. One simple way to start is standing up from a chair without using your arms. Strong muscles also offer the best protection against falls. We explain this in our guide to eating for longevity and in more detail in our guide to sarcopenia. If osteoporosis coincides with hormonal changes, see our menopause diet guide too.

Habits that gradually weaken your bones

Some habits increase calcium losses or gradually slow bone formation.

• Salt. When the kidneys remove sodium, calcium is lost along with it. The more salt you eat, the more calcium you lose in your urine.
• Cola drinks. Regular consumption has been associated with lower bone density, perhaps because of their phosphoric acid or because they replace milk.
• Large amounts of coffee and tea. From three or four cups a day, coffee and tea may slightly increase calcium loss in urine.
• Alcohol. It slows bone formation and worsens balance. Spanish guidelines recommend avoiding excessive drinking, as well as smoking [1].
• Crash diets. At Alimmenta, we do not recommend diets below 1,200 kcal a day. Below that level, medical supervision is needed because nutrient deficiencies may develop. In older adults, severe calorie restriction also encourages muscle loss [5]. If you need to lose weight, do so gradually with professional guidance, as we explain in our weight loss diet guide.
• Being underweight. A body mass index below 20 is a risk factor for fracture [1]. If you struggle to maintain your weight, a dietitian specialising in weight gain can help.

Do you need calcium or vitamin D supplements?

This is one of the questions we hear most often in consultations. For calcium, the European osteoporosis guideline prefers food and reserves supplements for people who cannot meet their needs through diet and are at high risk [3]. Calcium supplements can cause kidney stones and digestive discomfort, and the possible increase in cardiovascular risk is still debated [3]. Take them only if your doctor or dietitian recommends them after assessing what you eat.

Vitamin D supplements are common because winter sunlight, or spending little time outdoors, is not enough. Your doctor or dietitian recommends the supplement, usually after a 25-hydroxyvitamin D blood test.

No supplement replaces medication when fracture risk is high. Food and exercise provide the foundation on which that treatment works.

What mistakes do we see in consultations?

• Cutting out dairy for fear of fat or because it is said to “cause inflammation”, without replacing it. Daily calcium intake can fall sharply without anyone noticing.
• Having coffee and biscuits for breakfast and only fruit for dinner. Both meals contain very little protein or calcium, making it hard to catch up during the rest of the day.
• Walking as your only exercise. It helps, but bones and muscles also need strength work.
• Stopping all movement after a fracture for fear of another. This is when adapted, well-guided exercise is especially important.
• Losing weight by cutting back on dairy and protein. Weight falls, but some muscle and bone are lost too.
• Assuming diet no longer matters because you are receiving medical treatment. Osteoporosis treatments need to be accompanied by enough calcium and vitamin D [1].