Calcium is the most abundant mineral in the body and it’s not just there for making healthy bones. Calcium is needed to move muscles, send nerve signals and release hormones. While dairy gets a lot of the attention for being a good source of calcium, there are plenty of other foods that help meet your needs too. In today’s podcast, I’ll look at the roles of calcium, the consequences of not getting enough and tackle the controversial area of if calcium supplements are to be recommended or not.

Calcium is the most abundant mineral in the body, and you’ll find 99 percent of it in the bones and teeth. But calcium isn’t just there to give strength to bones, it also serves as a calcium bank, offering a readily available source of the mineral to the body fluids should a drop in blood calcium occur. So even though just 1 percent of the body’s calcium circulates in the extracellular and intracellular fluids, its presence there is vital to life

Calcium helps to maintain normal blood pressure, help with muscle contractions, the transmission of nerve impulses, secretion of hormones and the activation of some enzyme reactions. The blood borrows and returns calcium as needed so that even with a dietary deficiency, blood calcium remains normal – even as bone calcium diminishes. Someone can have an inadequate calcium intake for years and suffer no noticeable symptoms. Only later in life does it become apparent that bone integrity has been compromised.

On average, adults absorb about 30 percent of the calcium they take in. But this can change. For example, during pregnancy, a woman absorbs more calcium. Similarly, growing children absorb up to 60 percent of the calcium they consume.

Factors that enhance calcium absorption include having a good supply stomach acid, lactose and of course vitamin D. Factors that reduce calcium absorption include a high phosphorus intake, phytates found in seeds, nuts and grains and oxalates in foods like rhubarb and spinach.

Of course, milk and other dairy products are excellent sources of calcium, but many people, for a variety of reasons, cannot or do not want to drink milk. Some cultures do not use milk in their cuisines; some vegetarians exclude milk as well as meat, and some people are allergic to milk protein or are lactose intolerant. Others simply do not like the taste of milk.

Calcium-fortified soymilk is also an excellent substitute for cow’s milk in terms of providing an equivalent amount of calcium. Calcium can also be found in good amounts in plant-based foods such as bok choy, kale, parsley, broccoli and watercress. Some brands of tofu that have been set with calcium, nuts such as almonds and some seeds (such as sesame seeds and tahini) can supply calcium for the person who doesn’t consume dairy. Canned fish with bones can also be a great source of calcium.

With the exception of foods such as spinach that contain compounds like oxalate that can bind calcium and reduce its absorption to a large degree, the calcium content of foods is usually more important than its bioavailability. We absorb about half of the calcium from foods like cauliflower and broccoli. About 30 percent is absorbed from dairy foods and calcium-fortified foods. While about 20 percent is absorbed from foods like almonds and sweet potatoes. These are percentages though and what matters most is the absolute quantity of calcium in these foods and for that dairy foods are well in front. Of course, you don’t have to have dairy, but that doesn’t change that it is an excellent source of calcium.

Now, I sometimes hear and read comments that dairy causes calcium to be leached from bones and so it depletes calcium in the bones. While countries with the highest rates of osteoporosis have the highest rates of milk consumption. So, is it game over for dairy? Not at all.

Such comments if you come across them are very often used to justify a vegan diet. Now firstly, if you want to go vegan, fantastic. It can be a very healthy way of eating. And if you’re doing it for ethical or other reasons, that’s completely your call - this is a nutrition science podcast, I’m not ever going to preach to anyone on what ethics they should follow when it comes to food choices.

But when it comes to calling on nutrition science research to support a diet philosophy, then you should give a fair portrayal of the research, not just cherry-pick research that supports your agenda. I see the pro-vegan agenda used as a platform to call out any research that is funded by the dairy industry but fail to acknowledge their own biases in only providing a very selective view of the research or to equally call out research that is funded by the plant industry – for which there is a lot of.

So does dairy really leech calcium from bones and increase the risk of osteoporosis? Dairy most definitely does NOT leech calcium from bones - the calcium from dairy is absorbed very well and bioavailability studies show this.

Now, at a country population level, there is some link between countries that have higher intakes of milk consumption having higher rates of osteoporosis, but this is some of the lowest quality evidence as it cannot make allowances for all the other factors that are important in bone health – exercise is a big one here. Also, it could be that dairy is mostly drunk by people who have a low risk of osteoporosis and not much milk is consumed by people who have a high risk – these ecologic studies cannot tell you if that is the case.

When you look at higher levels of evidence at the level of what individuals are actually doing, dairy consumption is beneficial for bone health. Looking at the most recent systematic reviews and meta-analysis – these are the best types of studies - there is a clear favourable benefit of dairy consumption on bone health. A 2018 review published in Nutrition Research Reviews found an increase in bone mineral density and a reduction in fracture risk with increasing dairy consumption. An even more recent review and meta-analyses published in Advances in Nutrition in March 2019 found that a healthy diet that included milk and dairy was linked to less chance of having low bone mineral density or of having a fracture. As always, grab these studies in the show notes. https://pubmed.ncbi.nlm.nih.gov/29560832 and https://pubmed.ncbi.nlm.nih.gov/30657847 

So, some of those studies showing countries with high milk consumption having higher rates of osteoporosis are more-than-likely just measuring Western affluence of which low physical activity goes along with that.

In the end, you don't have to have dairy to be healthy, yet you can say the same thing about any food - no one food is essential. If you choose to include dairy foods in your diet, then there is nothing to be concerned about that these foods will somehow be bad for your bones.

Osteoporosis

That was a long segue into the topic of osteoporosis. Osteoporosis is actually more of a disease of youth rather than older age as a low calcium intake during the growing years limits the bones’ ability to reach their optimal mass and density. Most people achieve a peak bone mass by their late twenties, and dense bones best protect against age-related bone loss and fractures.

All adults lose bone as they grow older, beginning between the ages of 30 and 40. When bone losses reach the point of causing fractures under common, everyday stresses, the condition is known as osteoporosis. One in two women and one in three men over 60 years of age in Australia will develop an osteoporotic fracture. Unlike many diseases that make themselves known through symptoms such as pain, shortness of breath, skin lesions, tiredness and the like, osteoporosis is silent. The body sends no signals saying bones are losing their calcium to a dangerous fracture-risk level.

To maximise bone mass, the diet must deliver an adequate supply of calcium during the first three decades of life. Children and teens who get enough calcium and vitamin D have denser bones than those with inadequate intakes. With little or no calcium from the diet, the body must depend on bone to supply calcium to the blood – bone mass diminishes, and bones lose their density and strength. When people reach the bone-losing years of middle age, those who formed dense bones during their youth have the advantage. They simply have more bone starting out and can lose more before suffering ill effects.

And while dietary calcium gets a lot of focus here, physical activity may be the single most important factor supporting bone growth during adolescence. Muscle strength and bone strength go together. When muscles work, they pull on the bones, stimulating them to develop and grow denser. The hormones that promote new muscle growth also favour the building of bone. As a result, active bones are denser and stronger than sedentary bones.

A good example is gymnasts who undergo a lot of impact forces in their training - most often during childhood and their teenage years. They have bone-mineral densities much higher than their peers competing in other sports. For contrast, swimmers and cyclists have much lower bone densities because of the lower impact forces in their sport. But doing any sport or physical activity will be better for your bones than doing none.

Supplements

For people who cannot obtain adequate calcium from foods to meet their requirements, there is the option to consider taking calcium supplements. Most calcium supplements provide between 250 and 1000 milligrams of calcium. Calcium supplements are typically sold as compounds of calcium carbonate, citrate, gluconate, lactate, malate or phosphate. These supplements often include magnesium, vitamin D or both.

Supplements containing calcium carbonate require stomach acidity for optimal absorption and so are best taken with meals. People who suffer from reduced gastric acid production or are taking medications that inhibit gastric acid secretion are better off to take calcium citrate supplements rather than calcium carbonate.

The idea of recommending calcium supplements is a contentious one as the research evidence is very mixed that they offer much benefit in reducing the risk of osteoporosis, at least if vitamin D isn’t taken with them, and there even could be some downsides with some studies showing a greater risk of coronary artery calcification and heart disease as well as kidney stones.

There are contrasting medical views that people are better off focussing on exercise and vitamin D for bone health rather than taking calcium supplements when it comes to long-term osteoporosis and fracture risk. So, this is one area that you are best to seek advice on from your doctor if calcium supplements are appropriate for you. And if you want to read more about this controversial area, I’ve linked to a review paper in the show notes on the good, bad and ugly of calcium supplementation. https://pubmed.ncbi.nlm.nih.gov/30568435 

So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on if it supports it, or else head over to my webpage www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.

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I’m Tim Crowe and you’ve been listening to Thinking Nutrition.