We are all well aware of the importance of calcium for bone health. I want to clarify why calcium should not be the only thing considered when assessing supporting your bone health and density. When following a whole, real food eating plan, you are also probably probably getting more calcium than you think, and I am going to explain the how’s and why’s.
There are a number of considerations when discussing calcium. Primarily, it is important to assess your intake of fat-soluble vitamins, like A, D, and K – specifically K2. If you are consuming organ meats—particularly liver, lard, grass-fed butter, and maybe even some cod liver oil, you are already ahead of the curve in terms of the fat-soluble vitamins in your diet.
These fat-soluble vitamins are crucial for the deposition of calcium into bones to strengthen the mineral density and to fight fractures. Vitamin K2 for example, activates a protein called osteocalcin, which attracts calcium into bones and teeth. Without K2, the calcium you are ingesting has a difficult time knowing where to go and can remain circulating in your bloodstream. This can result in calcium being deposited onto the arterial walls. Molecules such as matrix GLA proteins, or MGPs, need vitamin K to function, and their purpose is also to help calcium get where it needs to go.
Your arteries are one of the places where you want to avoid calcium deposition, and these K2-dependent proteins are essential for moving calcium throughout the body to where it is needed and wanted which is not in the arteries. This is why a lack of Vitamin K2 can contribute to heart disease development: arteries can start to become calcified when calcium begins building up in them instead of being transported to your bones and teeth.
In order to produce osteocalcin (a non-collagenous protein found in bone and dentin) and MGPs, you need vitamin A, vitamin D. Vitamin K2 is the activator. Vitamin D is also required to activate calbindins, which are calcium-binding proteins in your intestinal cells. This means that if you are deficient in vitamin D, you cannot absorb all the calcium you are eating or supplementing with, because those proteins that take the calcium from our gut to other places in our body cannot be activated. It becomes simple to comprehend the necessity for the fat-soluble vitamins, A, D, and K2, to use calcium effectively, where it is needed the most. This is the foundation that needs to be addressed before discussing sources of calcium in the diet – you need these other vitamins to make sure any calcium you are ingesting is getting to where it needs to go, and being absorbed correctly and efficiently.
Supplementation of these vitamins is an option as lifestyle factors and geographical location can prevent you from getting adequate levels of Vitamin D naturally, from the sun. Liver and cod live oil are good a source of Vitamins A & D. Vitamin K2 is found in free-run eggs, natto, and cheese, particularly grass-fed cheese. If you are able to tolerate dairy, this is a solid source of Vitamin K2 and calcium (an example of nature providing us with nutrition and all the by-products needed to use it!!)
If you are not eating dairy products, there are a many foods that provide adequate calcium. Sardines and other bone-in fish are always excellent sources. Dark, leafy greens including spinach, bok choy, collards, kale and Swiss chard, as well as nuts and seeds, particularly sesame seeds, are great sources of calcium.
A high-protein diet has been shown to increase the absorption of calcium. If you are concerned with getting enough, making sure that your protein consumption is adequate. By avoiding grains and foods that are high in anti-nutrients like phytates and excessive oalates, your calcium absorption rate will be much higher and you will be able to make do with consuming a little less. Since phytates bind calcium, they prevent its absorption. This means that when, you consume calcium, but are also consuming phytate-containing foods, those phytates bind onto calcium, which then passes out of the body without absorbing it.
Eating calcium-rich foods in the context of a low-anti-nutrient diet, will result in a much higher absorption rate than on a standard American diet where grains and legumes, along with other anti-nutrient rich foods are consumed regularly, even in the presence of calcium. If you are getting adequate fat-soluble vitamins and eating green, leafy vegetables and some bone-in fish, and nuts and seeds on a regular basis, you are eating enough protein, and concentrating on good sources of fats, you are getting adequate amounts of calcium in your diet and metabolized by your body. Of course if you tolerate dairy, it is a really good way to get more calcium (specifically full-fat, organic) in your diet, but not necessary as long as you are following this type of protocol.
I do want to mention, since I think this is probably an add-on question that people might have about this topic, that I strongly encourage getting your calcium from food, as I am very wary of calcium supplementation. Studies have shown that calcium supplementation increases the risk of atherosclerosis, which is the hardening of the arteries. I would think this is due to the fact that people are just taking calcium alone without being concerned about the fat-soluble vitamins, especially when it is in the form of a calcium supplement. There is nothing else in there. This calcium might not end up where it is meant to, in the bones and teeth, and instead, ends up in the arteries as discussed. Even people that present real concerns regarding their calcium intake should do their best to get it from food, with a strong focus on those fat-soluble vitamins. Weight-bearing exercise and getting adequate sunlight are very important for bone health too.
At least 600mg per day of calcium from the diet should be adequate. This is a little lower than what the RDA of approximately 1000mg (up to 1,200 mg for women). These RDAs are based on a diet low in those fat-soluble vitamins that we were talking about, so if you are getting adequate vitamin A, vitamin D, vitamin K2, then I feel that 600mg per day could be enough. If you run your diet through an analysis tool, or have a professional assess your nutrient intake and it turns out you are eating less than 600mg per day and you are unable to eat foods that have high calcium amounts regularly (for you struggle to eat green vegetables due to IBD), then I do think that potentially supplementation can be helpful in certain cases. I want to stress that this is only to get you above that 600mg mark. There is no need to overdo it, and certainly this is not one of those supplements you should be taking unless you have a true an issue with getting it from food. If this applies to you, work with someone to determine how to go about supplementing in a way that would be beneficial and ensure that the calcium is getting transported into the bones and not just floating around your bloodstream. There are many factors involved in good bone density and certainly calcium is one of them, but it is not the only factor.
Another issue to be aware of if you are consuming the majority of your calcium from leafy greens is further anti-nutrients that can block the absorption of calcium. This includes the aforementioned phytates and oxalates. If most of your calcium is from those plant foods, you are probably not absorbing it as much as you think, or, alternately, you will need to eat really large amounts.
On a vegetarian or vegan diet getting sufficient can be a challenge, but even for omnivores, the leafy greens and vegetarian sources, like nuts and seeds can pose hurdles. For example, sesame seeds are pretty high in calcium, but do have some of those anti-nutrients. Decreasing the amount of grains you are eating is a way to mitigate this effect as they are the highest source of phytates and eating those along with your leafy greens will have a negative impact on calcium absorption.
Bone-in fish is really the optimal calcium source. This can include canned of salmon with the bones in, or sardines that have the bones in. Furthermore, you will be getting vitamin D from the fatty fish - both the bioavailable calcium and the fat-soluble vitamin that will help absorb it in one small package.
Below are some charts indicating the amount of calcium in certain serving sizes of foods: