Eating calcium-rich food is essential for bone health. But not all sources of calcium are equal.
This article takes a look at
- the importance of calcium to your health
- why calcium matters to your bone health – now and in the future
- how much calcium you need
- the different calcium food sources
- why not all foods high in calcium are good sources
- choosing good dairy-free sources of calcium
- how to get enough calcium if you’re gluten free
In the UK most of us rely on wheat and dairy for calcium
Wheat and dairy are the two main sources of calcium in the UK diet (1). Dairy is a naturally calcium-rich food. Whereas wheat flour is fortified to make it a good calcium source. And together these two calcium-rich foods provide two-thirds of our intake.
But increasing numbers of people are cutting back on their dairy consumption for ethical reasons (2). And others are choosing gluten-free and avoiding wheat on health grounds.
Yet cutting wheat or dairy out of your diet needs careful thought. Otherwise, you could dramatically reduce your calcium intake. And consuming enough calcium is crucial to your long-term bone health.
What’s more, calcium deficiency has no early signs.
Cutting back on wheat or dairy may be a choice or a necessity. But in either case, it’s vital you replace them with alternative calcium sources.
Calcium and your bones
Calcium is the most abundant mineral in your body – your adult body contains more than a kilo (3). And 99% that calcium is in your bones and teeth. The remaining 1% is dissolved in your blood and the fluid between your cells.
Your bones are ever changing
We think of our skeleton as the scaffolding of our body. And calcium gives that scaffolding strength. But unlike metal scaffolding tubes our bones aren’t inert. They’re living and dynamic.
Your bones are being constantly remodelled in an endless cycle of formation and reabsorption. It’s a process known as bone turnover. And as part of that process your bones assimilate and release calcium.
Bone turnover continues throughout your life. Still, there are three distinct phases.
- As a child or young adult, your growing body makes more bone than it reabsorbs. Your bone mass steadily increases reaching its peak around twenty-five years old. And the final peak bone mass you attain is critical to your long-term bone health.
- Between the ages of twenty-five to thirty-five bone formation matches reabsorption. All things being equal, your bone mass remains constant.
- From thirty-five onwards, bone reabsorption outstrips formation. And your bone mass steadily decreases as you age.
The exact timing may vary by a year or two between individuals. But the bone mass trajectory is the same for everyone. But there’s one important difference between the sexes. Changes in hormone levels increase the rate of decline in postmenopausal women. And ladies, this makes attaining your maximum peak bone mass even more important.
The importance of reaching your maximum potential bone mass
Still, regardless of your gender, achieving your maximum potential bone mass matters. Having large reserves of bone strength helps you weather the inevitable decline.
And adding smart lifestyle choices will slow bone mass decline.
Starting from the highest peak and slowing the descent is a powerful combination. A combination that can save you from brittle bones and osteoporosis in later life.
Lifestyle impacts your bone mass and risk of osteoporosis
Your lifestyle has a significant influence on your bone mass. And that has an impact on your risk of osteoporosis in old age.
Some osteoporosis risk factors you can’t change including
- gender – women have a higher risk
- age – the risk increases with age
- family history
But your lifestyle has the greatest influence your bone health and osteoporosis risk.
Lifestyle components that increase peak bone mass and slow bone loss are
- Sufficient dietary calcium
- Adequate vitamin D (by exposure to sunshine or supplementation)
- Physical activity, especially strength training
Lifestyle causes of lower peak bone mass and increased bone loss are
- heavy drinking
- being underweight
Calcium – the 1% keeping your body functioning -and why it matters to your bone health
The tiny amount of calcium not in your bones has many functions
The calcium outside your bones is dissolved in your blood and the fluid between your cells. It only amounts to seemingly insignificant 1%. Yet it’s critical to many vital metabolic processes, including
- muscle contractions
- nerve impulses
- blood clotting
- signalling inside your cells
- red and white blood cells formation
How your body manages a deficit of calcium
Because so much relies on this tiny amount of calcium, your body must tightly control the levels. If it didn’t, you’d quickly become very ill. But unlike other minerals, your body has a huge reservoir of calcium – your bones.
When you don’t eat enough calcium your body dips into this reservoir to keep your body functioning. It’s a system designed to balance out daily variations in your calcium intake.
A few days of low calcium intake is harmless. The calcium “borrowed” from your bones will be replaced. But a diet habitually poor in calcium has long-term consequences.
Your body prioritises short-term survival over long-term health. Without enough calcium, it maintains normal blood levels at the expense of bone integrity.
As a result, calcium deficiency can have no early signs. You look and feel normal as the reservoir of calcium in your bones slowly diminishes.
The health consequences of low dietary calcium
If the body is unable to maintain blood calcium levels it causes hypocalcaemia, also known as calcium deficiency disease. It happens when calcium levels are so low, no more can be drawn from the bones.
And without enough dissolved calcium the body normal body functions breakdown.
Left untreated it’s a potentially life-threatening condition.
- Extreme fatigue
- Muscle aches, cramps and spasms
- Numbness and tingling in the arms, hands, legs and feet
Hypocalcaemia needs prompt medical intervention to avoid complications.
The two most common causes of rickets are a lack of calcium or a lack of vitamin D.
It’s a condition that affects a child’s bone development. Poor bone growth leads to pain, soft and weak bones and ultimately bone deformities.
Rickets isn’t that common in the UK. But recent studies suggest the number of cases is increasing (4).
Most children are successfully treated with improvements to calcium or v
A calcium deficiency in adults causes a similar condition called osteopenia.
Osteopenia is the clinical term for “soft bones”. In other words, a lower than normal bone density. There are no symptoms. But lower bone density can increase your chances of breaking a bone.
And having osteopenia increases your risk of osteoporosis as you age.
Osteoporosis is a separate diagnosis from osteopenia.
The bone’s external walls are thinner and the internal framework has degraded. And this makes the bones weaker. Like osteopenia, there aren’t any symptoms. Often the first sign is breaking a bone.
Women have a higher risk of osteoporosis due to the hormone changes of the menopause. The fall in oestrogen causes a steep increase in bone loss for between five and ten years. The speed of decline does slow. But there’s significantly less bone mass to see out the remaining years. When the pre-menopause bone mass isn’t enough to absorb the years of steep decline it causes osteoporosis.
Osteoporosis can have consequences beyond the pain of a broken bone. Something as serious as a hip fracture can take a long time to heal and can have complications. The legacy is often impaired mobility, decreased confidence and reduced quality of life.
How much calcium do you need?
The amount of calcium you need depends on your age. The intakes recommended by the UK Department of Health are
- Infants under 1yr – 525mg
- 1-3yrs – 350mg
- 4-6yrs – 450mg
- 7-10yrs – 550mg
- Boys 11-18 – 1000mg
- Girls 11-18 – 800mg
- Adults over 18yrs – 700mg
- Breastfeeding mums – 1250mg
Most people eating the typical British diet – whatever that is – eat enough calcium. The exception is adolescents. Most adolescent boys’ and girls’ calcium intake is less than recommended.
The adult recommendations are 700mg of calcium per day. But the average adult loses only 200mg/day of calcium in sweat, hair, bile and urine. That’s a big difference.
The dietary recommendation is so much higher because calcium absorption is inefficient. To be sure you can absorb enough, you must eat a lot. Up to five times more than you lose.
Your gut starts preparing calcium for absorption in your stomach.
The first step is dissolving the calcium in the liquid contents of the intestine. The more accessible calcium in foods like dairy starts dissolving in your stomach. But whole plant foods like kale or nuts need a bit more digestion before your gut can access their calcium.
But no matter the source, only dissolved calcium is absorbed.
Calcium Absorption is inefficient
Most calcium uptake happens in the small intestine with a little in the colon. Yet calcium uptake is not terribly efficient. Only between 20-50% of the calcium you eat is absorbed. What your gut doesn’t absorb is flushed down the toilet.
The proportion depends on the amount in your diet and the needs of your body. And those needs change over a lifetime.
Children with their fast-growing bones can reach absorption rates of 75%. And a mother’s calcium uptake doubles during pregnancy (5).
The UK dietary guidelines take our inefficient calcium uptake into account. And they allow for our changing needs over the life course. Follow them and you’re likely to consume enough calcium to replace your daily losses. And to attain your maximum potential peak bone mass if that’s your life stage.
But the guidelines assume your eating habits follow a typical British diet. And that means a heavy reliance on dairy and cereals.
And if you follow a dairy-free or gluten-free diet you may need to consume more than the normal calcium recommendation. Because not all sources share the high calcium absorption rates of dairy and cereals.
So, how much calcium your gut can absorb from a food? It depends on its bioavailability.
How easily your gut can absorb a nutrient is known as its bioavailability.
Calcium bioavailability is influenced by the food source and the form of calcium. For example, 30% of the calcium in milk can be absorbed but only 5% from spinach(6).
Bioavailability is critical if there isn’t much calcium in your diet. But it’s less significance if dietary calcium is plentiful (7).
Excluding dairy or wheat from your diet could reduce its overall calcium bioavailability. Including fortified alternatives is a good option. But calcium fortification can be variable as it isn’t mandatory.
If you’re relying on unfortified vegetable and nut sources you’ll need to plan your diet carefully. Many of these foods are high calcium. Yet the bioavailability is low because they contain potent absorption inhibitors.
Calcium absorption inhibitors
Oxalates and phytates
Oxalates and phytates inhibit the
Oxalates are the most powerful calcium absorption inhibitors. They’re compounds found in fruits, nuts and vegetables – especially leafy greens.
Phytates are antioxidant compounds found in seeds, nuts, cereals, legumes and to a lesser extent in vegetables. Phytates and other antioxidants are beneficial to your health. But phytates do inhibit calcium uptake.
Both oxalates and phytates bind the calcium in your gut into insoluble molecules. And this prevents calcium absorption.
And the higher the inhibitor’s concentration the lower the calcium bioavailability of the food. Foods with very high levels, like rhubarb, can even reduce the absorbable calcium of your meal’s other ingredients.
Take spinach. It’s high in calcium but it’s also high in oxalates and phytates. As a result, it not a good source(8).
An exception to this general rule is soybeans. They’re a better source of calcium than their oxalate and phytate content would suggest (9).
Plants’ oxalate and phytate content are highest when they’re raw. If you soak, boil or steam them it lowers the inhibitor concentration. Calcium bioavailability is improved. But at the same time, other nutrients, like vitamin C, can be reduced.
Phosphorus is plentiful in most foods. And the dietary calcium-phosphorus ratio’s influence on calcium uptake is debated. Yes, this ratio has been shown to influence calcium absorption. But real-life fluctuations outside the lab don’t significantly affect uptake (10).
The role of fibre in calcium absorption is controversial. It may be that fibre reduces absorption. Or that the high oxalate and phytate content of high fibre foods reduce calcium bioavailability (11).
Established research has concentrated on the uptake of calcium in the small intestine. But it has ignored the significance of absorption in the colon (12). This approach is now being challenged.
More recent research into the gut microbiome – the trillions of bacteria that inhabit your gut – links prebiotic fibres with enhanced calcium absorption and improved bone health (13).
Eating a high fibre, prebiotic diet encourages a healthy population of gut bacteria. And that may actually improve your calcium uptake.
The two mechanisms of calcium absorption
Your gut has two calcium uptake systems (14). A passive system and an active energy dependent system. The importance of each depends on your dietary intake.
Passive calcium absorption
Passive absorption is the main method of calcium uptake when your dietary intake is adequate or high. And with plenty available calcium your body reduces active calcium uptake.
Active calcium absorption
If your intake is low your body turns up active calcium absorption to help it get the calcium it needs. This active uptake becomes more important than passive absorption. It’s a process that needs energy to drive it. And it’s totally dependent on your body having enough vitamin D.
Vitamin D plays several roles in preserving your body’s calcium balance. It’s involved in bone turnover and remodelling. Both in bone formation and reabsorption. It helps maintain the delicate soluble calcium equilibrium keeping your body function normally. And it’s required for active calcium absorption.
Vitamin D controls a specialized calcium-binding protein that enables active absorption. The v
Dairy and Calcium
Why do we rely on dairy for calcium?
In most countries, including the UK, we rely heavily on dairy products for our calcium. But why?
After all, before animals were domesticated, humans didn’t drink any milk after weaning. Dairy only became a staple of the human diet with the advent of agriculture around ten thousand years ago.
The emergence of farming also marked a move away from a diet dominated by low-energy plant foods towards a reliance on grain. Grain is a high energy food. But it’s a relatively poor source of calcium.
The anthropological evidence suggests our hunter-gatherer ancestors ate prodigious amounts of low-energy plant foods. And this diet provided substantially more calcium than the UK dietary recommendations (15).
The introduction of agriculture created a parallel reliance on dairy and grain. And in doing so dairy replaced plants as our main source of calcium.
Ten thousand years of agriculture has shaped our society and our diet. Even if you wanted to, it isn’t possible to replicate the predominantly wild plant diet of our hunter-gatherer ancestors. Sorry, Paleo diehards – it’s the truth.
As a society, we rely heavily on dairy. And cutting dairy from your diet makes getting enough calcium more challenging.
Dairy is an excellent source of Calcium
Dairy has a reputation as one of the best sources of calcium. And it’s deserved.
Milk starts with
This combination of high concentration, bioavailability and portion contribution are important. They make milk the calcium standard to compare all other foods against.
And processing milk doesn’t diminish the bioavailability. Dairy products like cheese and yoghurt share milk’s high standard.
How much of the calcium in the UK diet comes from dairy?
Dairy is the major source of calcium in the UK diet. It provides adults with over a third of the calcium they need (16). Most of that comes from milk and cream. Cheese is the other big source. 7% of our daily calcium intake comes just from cheddar!
And milk is even more important to children. Dairy provides over half of a toddlers’ calcium – most of it from milk (17). As children grow up and expand their diet, they rely a little less on milk for their calcium needs. But as fast-growing adolescents, this reduced milk intake is potentially detrimental. Without milk, they can struggle to eat enough calcium for their developing bones.
Dairy Alternatives aren’t guaranteed to contain much calcium
Consumer demand for non-dairy alternatives has increased availability. You now have a wide choice of non-dairy milks, yoghurts and cheese. But these products don’t naturally contain as much calcium as true dairy.
If you are doing a like for like swap to dairy-free, read the labels carefully. Some dairy alternatives are fortified with calcium. But fortification is voluntary, so not all manufacturers add calcium. And fortification rates are not uniform. The Alpro brand does fortify their yoghurts and milk alternatives.
As yet, I haven’t come across any calcium-fortified, dairy-free cheeses.
The importance of wheat
Grains are not naturally high in calcium. Yet almost another third of UK calcium intake comes from cereal products. More specifically wheat flour.
Since the second world war calcium has been added to wheat flour. Today, UK manufacturers are legally required to all fortify wheat flours except wholemeal.
By law, flour is fortified with iron, thiamine, niacin and calcium.
Most flours have the highly nutritious germ and bran removed in the milling process. Fortification replaces some of the lost nutrients. The legal requirement for calcium is 235-390mg/100 grams (18).
Fortification makes flour a great source of calcium. Unfortunately, most flour is used to produce highly processed foods. Foods with little nutritional benefit beyond fortification to recommend them.
Wholemeal flour, as the name suggests, is made from the whole grain. Keeping the germ and bran retains the micronutrient content of the flour.
Consequently, fortification isn’t a legal requirement for wholemeal flour. And wholemeal has a little less calcium than its refined, fortified cousin. But the bioavailability of the calcium is higher. That makes it a better source of calcium.
One more reason I’d recommend grabbing the wholemeal and leaving the white flour on the shelf.
Gluten-free and calcium
Around 1% of the UK population has coeliac disease (19), a serious, life-long autoimmune condition. Coeliac disease is treated by excluding gluten from the diet. However, many more people exclude some or all wheat from their diet on health grounds (20).
This increased demand has driven an explosion in gluten-free products in our supermarkets. And they taste far better than they used to – great news for coeliacs. But because there’s no legal requirement for fortification, very few are (21).
On a gluten-free diet, you can’t rely on bread or pasta substitutes for your calcium intake. Read the labels carefully. Fortification is voluntary and not universal.
What makes a good non-dairy or gluten-free source of calcium?
And a normal portion needs to make a significant calcium contribution to your diet.
Take black peppercorns. They’re one of my favourite seasonings. And black pepper packs a mighty impressive 443mg of calcium per 100g. That’s more than half the daily recommendation! But a few twists of a pepper mill over your food is only 0.1-0.2g. And that’s only worth around 0.5mg of calcium. Not such an impressive calcium source after all!
Comparing calcium sources
The table below compares the bioavailability of allegedly good sources of calcium with dairy and wheat flour (bread).
Calcium content is well documented for most foods. And most recommendations
There’s less data on the calcium bioavailability than calcium content. And there are significant gaps in the knowledge. The table is only a guide to the absorbable calcium in typical portions of different types of foods. Still, it will help you make a more informed choice about your sources of dietary calcium.
Foods that are a good source of calcium are highlighted in green. A good source of calcium is defined as 30mg of bioavailable calcium both per serving and per 100 calories (22).
Using a glass of milk to make sense of the calcium content
A glass of milk is a good benchmark. You can see that three glasses comfortably exceed the daily recommended intake (700mg). And because of the high bioavailability, just two are enough to replace your daily calcium losses (200mg).
So, to help put the calcium content of the other foods in perspective, I’ve compared them all to a glass of milk.
And it’s easy to see how a cheese sandwich can make a significant contribution to your calcium intake. But is eating 16 portions of spinach a day a realistic alternative to a glass of milk? Or how about seven sweet potatoes?
Breakfast cereals aren’t in the table. Many are fortified. But there is no standard or legal requirement. If they’re made with refined wheat flour they definitely will be fortified. But that probably makes them a poor choice for all sorts of other nutritional reasons. The only answer is to read the label carefully.
Beans and legumes are high in phytates. And that impacts their calcium bioavailability. Some are still a reasonable source of calcium. But you need to be prepared to eat multiple portions per day.
Brassicas (broccoli, cabbage etc) are relatively low in oxalates and phytates. And that’s why even despite containing less calcium they are better sources of calcium than spinach.
Some seeds and nuts are high calcium, but this can be deceptive. For example, chia seeds have an impressive 567mg per 100g – but a puny bioavailability of only 2.8% (28). And t
Almonds are one of the best nut sources. But you can see you
Most tofu is set using calcium salts. And this can make tofu a good source of calcium. But not all are set using the same technique. Check the label. If it’s not calcium set it won’t have similar levels to the table.
Tinned sardines are cheap health food full of nutrients. I love them. But I can see why they’re not everyone’s cup of tea. Yet, they’re a great source of calcium because of the tiny, cooked bones.
Summing up your choices
Dairy and wheat products are the easiest options to get the calcium you need. And they’re the simplest way to give your children the essential calcium for healthy bone growth.
But if you cut dairy, wheat or both from your diet, you must think carefully about where you’ll find your calcium.
Fortified alternatives are a good option. But read the labels carefully. Not all have added calcium.
Getting enough calcium from natural plant sources is certainly possible. But to absorb enough calcium you should aim to eat significantly more than the normal UK daily recommendations.
And it’s a commitment to eating much higher quantities of low-energy plant foods than most of us are willing to do. Especially children.
There’s no right or wrong choice. You have to decide what works for you and your family. And I hope this article has helped you understand your options.
Calcium is essential for your health. Just make sure you’re getting enough.
Hi, I’m Ralph – a nutritionist with over 25 years’ experience as a professional chef. I’m based in Edinburgh where I provide one-to-one nutrition coaching. If you’re not in Edinburgh I can help you online.