Thread: Minerals

How Much Calcium Do We Need?

The RDA is 1000 milligrams per day (mg/d) for most people over the age of 3. It increases to 1300 for children aged 9-18 to account for increased growth, and to 1200 for women over the age of 50 and men over the age of 70. The RDA is 200 mg/d during the first six months of life, 260 during the next six, and 700 mg between the ages of 1-3.

While not without controversy, the calcium RDAs are among the best supported by large amounts of evidence. Many people object that the only way to get the RDA is to drink milk, and many human societies have thrived without using milk. But there are many other sources of calcium. In the Arctic, for example, where there are no cows and plant foods are limited, the natives ate dried, pulverized fish bones. In Africa, a group of hunter-gatherers known as the Hadza consume large amounts of baobab. This is a plant with more calcium than milk, is considered a "food group," and makes up over 20 percent of their diet. Similarly, the Native Americans of the Northern Plains ate stinging nettles, which is much higher in calcium than milk. Each culture found prized sources of calcium-rich foods and made them critical parts of their traditional diets. Ours is dairy, and if we leave dairy behind we need to find another.

Calcium Absorption From Different Foods

Most foods have some calcium in them, and many besides milk have a lot.

But then... there is absorption.

We absorb calcium from food much better when we get enough vitamin D. Nevertheless, for a given amount of vitamin D, the absorbability of calcium differs greatly among different foods:

A little over 30% of the calcium in milk is absorbed. Edible bones have not been tested but they are probably similar.
40-60% of the calcium in most cruciferous vegetables is absorbed. These are foods like broccoli, kale, and bok choy.
20-25% of the calcium in legumes is absorbed.
Rhubarb (9%) and spinach (5%) have very poor absorbability.
Unfortunately, there are a tremendous number of foods where we don't know for sure how absorbable the calcium is. Let's start by looking at foods where it's been directly measured, then make some guesses about the rest of the foods we eat.

To meet the RDA, children up to 3 years old need the equivalent of two 8-ounce glasses of milk. Most adults need three glasses, while children and adolescents 9-18, women over 50, and men over 70 need four glasses. This would provide everyone with calcium within 100 milligrams of the target, which would be filled in by the other foods they consume.

For foods where the absorption has been directly measured in humans, these are each the equivalent of one 8-ounce glass of milk (or the same amount of yogurt or kefir). The veggies are measured after cooking:

40 grams of (g) cheddar cheese
90 g napa cabbage
100 g Chinese mustard greens
190 g bok choy
270 g kale
290 g Chinese spinach
320 g broccoli
430 g white beans
700 g pinto beans
790 g rhubarb
1.4 kilograms of (kg) spinach
1.6 kg sweet potatoes
1.7 kg red beans
Of the plant foods, the most practical to use is Chinese mustard greens. 100 g is a little over two-thirds of a cup. It would require just over 2 cups, measured after cooking, to yield the equivalent of 3 cups of milk. Close behind is napa cabbage. 90 g is three-quarters of a cup. Just under 2.3 cups yields the equivalent of 3-milks-a-day. 190 g boy choy is a little over one cup. 3.4 cups of it will meet the target.

Going further down the list starts to become impractical. For example, it would take over 6 cups of kale or broccoli to meet the target.

One of the most common traditional sources of calcium in dairy-free cultures has been bones. You can gnaw the ends off the small bones in a roast chicken. You can eat the bones in canned sardines or canned salmon. As mentioned before, the natives of the Arctic would dry and pulverize fish bones to get their calcium. Although no one has directly measured how much calcium humans absorb from edible bones, we have good reason to think that it is similar to milk. First, most calcium is present in bone bound to phosphate. The absorption of calcium phosphate has been tested in humans, and it's about 25%, a little less than the 32% we absorb from milk. Second, in lab animals, the proteins found in bone increase the absorption of the calcium. So we humans probably absorb the calcium from bone at least as well as we do from milk. We can obtain our three-milks-a-day target from bone, then, by consuming just over two-thirds of a teaspoon of powdered bone. If you eat canned fish, count each 30% of the daily value for calcium as one glass of milk.

Putting this altogether, your best bet is to mix and match three of any of the following foods each day:

One cup of milk, yogurt, or kefir.

One serving of canned fish providing 30% of the daily value of calcium.

One cup of Chinese mustard greens, napa cabbage, or bok choy.

So far we have been limiting our scope to the foods where the absorption has been directly measured.

We can broaden our scope by making some reasonable guesses about how much we absorb from other foods. The most important inhibitor of calcium absorption in plants is oxalate. This is the same oxalate that we talked about causing kidney stones in part 1. Let's assume that most low-oxalate vegetables have similar calcium absorbability. Let's also assume that most nuts, seeds, and beans have similar absorbability as the beans that have been measured.

The following foods should be equivalent to one cup of milk:

100 g sesame seeds, hull included
150 g chia seeds
180 g flax seeds
200 g typical tahini
270 g almonds
290 g Brazil nuts
These options, while helpful, are quite impractical to rely on because of the amount of calories they supply. Calories (Cal) are units of energy, and too many will make you fat! Plus you can only fit so many in your tummy at a time. A cup of full-fat milk has 146 Cal and low-fat milk has even less. 150 g chia seeds has 729 Cal and 200 g of tahini has 1190 Cal!

This brings us back to our original conclusions: mix-and-match dairy, bones, or the top three greens (Chinese mustard, napa cabbage, or bok choy) to get your calcium. If you have space for the calories, you can replace one of those with some of the nuts and seeds. If you have space for the volume, you can replace one of those with some of the other vegetables.

Calcium in Mineral Water

Before we talk supplements, let's talk about one thing that's not really a food or a supplement: mineral water. The minerals in mineral water are fully dissolved, and are likely very well absorbed. For example, Gerolsteiner and Ferrarelle have more than a cup of milk's worth of calcium per liter. Perrier, Uliveto, San Pellegrino, and Lete have a little under half that.

Calcium Supplements: Safety Concerns

Calcium supplements are a mostly safe and effective way to bring your intake up to the target.

There are a few special concerns, however:

In supplemental form, calcium might enter your system too quickly and promote soft tissue calcification.
Calcium supplements sometimes cause "calcium-alkali syndrome."
This syndrome can make you unusually thirsty and pee too much. It can make your heart beat more slowly, skip a beat, or flutter. It may make you confused, weak, or depressed.

Typically the person who develops this syndrome fits these criteria:

She is a woman who is elderly, pregnant, or bulimic.
She is also taking antacids, nonsteroidal anti-inflammatory drugs (NSAIDs, such as aspirin or Advil) or medications to manage blood pressure and swelling.
Her calcium supplement is calcium carbonate, oxide, or hydroxide.
We can avoid the risk of soft tissue calcification and calcium-alkali syndrome by sticking to some easy rules:

Use calcium supplements to help you meet the RDA when you cannot do so with food alone. Don't use supplements to exceed the RDA.

They will hit your system more slowly, like food, if you mix them into your food. If you don't want to mix it, take it at the end of your meal.

Always spread your calcium evenly across 3-4 meals.

Don't use carbonate, oxide, or hydroxide.

If you fit the other criteria for calcium-alkali syndrome, keep your total intake under 1000 mg/d and discuss your supplement with your doctor.

Calcium Supplements: Which Forms Are Best?

There are an incredible number of forms that calcium supplements come in, so rather than discuss every single one in detail, we'll cover them in groups.

BONE MEAL / MCHC / MCHA

This form is a traditional food, like the pulverized fish bones the natives of the Arctic used. Bone can be contaminated with lead, so look for manufacturers that test and disclose the contaminants. This is a good default for most people. It contains many proteins and traces of non-calcium non-phosphorus minerals that support bone health. Bone meal might be poorly absorbed in those with low stomach acid, and it is too high in phosphorus for people who need to avoid it. It is rich in collagen, which supports healthy hair, skin, and nails. Most people could use more of it. However, people who develop calcium oxalate kidney stones may benefit from avoiding collagen. MCHC and MCHA are other names for bone meal.

CALCIUM PHOSPHATE

Examples include tricalcium phosphate and dicalcium phosphate dihydrate. These are similar to the calcium in bone meal, but without the protein and extra minerals. They are less nourishing as a result, and they still can't be used by people who need to avoid phosphorus, but they would be better than bone meal for people who need to avoid collagen.

CALCIUM CITRATE, MALATE, LACTATE, GLUCONATE, GLUBIONATE, SULFATE, & GLYCEROPHOSPHATE

All of these forms are highly absorbable, and all of them except glycerophosphate are good for people who need to avoid phosphorus. Calcium citrate is better studied and more popular than the others, giving it a good safety record. The citrate is helpful for kidney stone prevention.

CALCIUM CARBONATE, HYDROXIDE, AND OXIDE

These are popular because they are cheap, especially calcium carbonate. They lack phosphorus and collagen, which can be advantageous for some people, but they account for most reports of calcium-alkali syndrome, suggesting they are less safe than other forms.

OYSTER SHELL, EGG SHELL, CORAL CALCIUM, DOLOMITE

These are all mostly calcium carbonate. Since they are natural, they have the advantage of proteins (except dolomite) and other minerals, and the disadvantage of possible contaminants. Since they contain calcium carbonate, they may carry the same risk of calcium-alkali syndrome.

The bottom line:

Use a bone meal if you have no need to avoid collagen or phosphorus. Choose a product where the contaminants are measured and disclosed.

Use calcium citrate if you need to avoid collagen or phosphorus, especially if you are at high risk of kidney stones.

How Much Phosphorus Do We Need?

Phosphorus is a simpler discussion. Most people actually get too much. In part one, we pointed out how only 1% of our calcium but a full 15% of our phosphorus is found outside of our bones. This much wider distribution of phosphorus means it's found in far more foods, is much easier to obtain, and far less likely to run deficient.

The RDA for phosphorus for all adults is 700 mg/d. For children older than one and for adolescents, the RDA is adjusted according to their needs for growth and age-related differences in how well they absorb phosphorus from food. It is 460 mg/d for children 1-3, 500 mg/d for children 4-8, and 1250 mg/d for adolescents 9-18. For infants, there wasn't enough evidence for an RDA, so they set an "everyone-is-doing-it-so-it-must-be-ok," also known as an "adequate intake (AI)," of 100 mg/d for the first six months of life and 275 mg/d for the next six months. This is based on what infants were consuming in milk and baby food.

It's Hard to Become Deficient in Phosphorus

When consuming natural foods, it is nearly impossible to become deficient in phosphorus. For simplicity, let's consider the adult target of 700 mg/d.

These are what you'd get if you ate 2,000 Calories (typical for an average daily intake) of a single food group all on its own:

Dairy: 2,600 mg.
Eggs: 2,100 mg.
Meat, poultry, or fish: 1700 mg.
Legumes, nuts, or seeds: 1600 mg.
Veggies 1100 mg.
Grains: 1050 mg.
Fruits: 608 mg.
What do Fruitarians, Refined Flour-Heads, and Keto-Carnivores Have in Common?

Ok, so strict fruitarians might be at risk. But the least of a fruitarian's problems will be phosphorus. In fact, their phosphorus intake would be amazing compared to their calcium intake.

A more dangerous dietary pattern would be the fat-bomber. 2000 Calories of fat only provides about 150 mg of phosphorus.

Keto dieters can get plenty from animal products and low-carb veggies. Carnivores can get plenty from meat. The potential problem would be with keto carnivores. The phosphorus requirement could be met with 550 Calories of dairy, 670 Calories of eggs, or 850 Calories of meat, poultry, or fish. But just animal fat wouldn't cut it.

In theory, someone could develop a moderate phosphorus deficiency from relying exclusively on refined flour. 2000 Calories of white flour only provides 593 mg of phosphorus. As with fruitarianism, though, the phosphorus actually looks really good on that diet compared to many other nutrients, including calcium. As we will see soon, though, most white flour products are full of hidden phosphorus.

Starvation, Refeeding, and Hungry Bones

There is one way to become deficient in phosphorus: don't eat. Starvation and eating disorders can lead to extended periods of time with little or no phosphorus consumed, and breakdown of lean mass that allows stored phosphorus to be lost in the urine. Rapid refeeding, especially with poor-quality food, causes phosphorus to get sucked up into the muscles, which causes blood levels to drop to dangerous levels. This is called "refeeding syndrome" and it can also affect magnesium and potassium. The best way to keep phosphorus levels up is to eat lots of meat and eggs.

Something similar happens after medical correction of a disorder causing bone loss. Phosphorus, calcium, and magnesium all get swept up into bones, and the blood levels drop. This is called "hungry bone syndrome" and dairy products are the best remedy.

Meat and eggs are the best match for refeeding syndrome because the phosphorus is going into the muscles where it doesn't need calcium, and meat and eggs provide phosphorus without calcium. Dairy is the best match for hungry bone syndrome, because the phosphorus is going into the bones where it does need calcium, and dairy provides both minerals.

Hidden Phosphorus Additives in Processed Foods

Overwhelmingly, most of us are likely to get too much phosphorus, not too little. The average intake in the United States is almost twice the RDA. Nearly 500 mg/d come from unlabeled food additives!

Phosphorus is added in large amounts to cola, anything with baking powder, and processed, parmesan, or American cheese.

Phosphorus is usually added to the following products:

anything with baker's yeast
cocoa powder
non-perishable fruit juice
vegetable spreads for bread
cold cuts, hot dogs, and sausages
Phosphorus is sometimes added to these:

frozen meat
canned seafood
many cheeses
yoghurt
chocolate
beer
instant coffee
These additives are very often unlabeled. Worse, studies suggest that ONLY these hidden additives hurt bone health. Meat seems neutral and dairy beneficial.

So the end result:

We can get enough phosphorus by eating a mix of natural whole foods.

We can avoid too much phosphorus by avoiding processed foods.

There's no need for supplements. Just meat and eggs for refeeding syndrome, and dairy for hungry bone syndrome.

Wrapping It All Up

All right, let's wrap up our three-part series on vitamin D, calcium, and phosphorus:

Deficiencies of vitamin D, calcium, or phosphorus contribute to rickets and osteomalacia.

Deficiencies of calcium or vitamin D contribute to tetany.

Toxicities of all three cause soft tissue calcification.

Toxicities of vitamin D or phosphorus cause weak, porous bones; calcium toxicity causes hard, brittle bones.

Most of us lie in the middle where calcium and vitamin D are on one team and phosphorus is on the other.

In this middle area, calcium and vitamin D protect against osteopenia and osteoporosis; phosphorus makes these diseases worse.

We also want "team calcium and vitamin D" for blood pressure, asthma, allergies, colds and flu, autoimmunity, insomnia, hormones, heart disease, and cancer.

Our best sources of vitamin D are sunshine, pastured egg yolks, cod liver oil, certain fish, or certain mushrooms (the mushrooms contain D2, possibly less effective than D3).

Sunshine is best mid-day, and this matters most outside of the summer and far from the equator.

The darker your skin, the more time you need in the sun, or the more you should focus on exposing more skin and lying down.

The best sources of calcium are dairy, bones, napa cabbage, Chinese mustard greens, bok choy, and high-calcium mineral water. Mix and match two for young kids, three for most adults, or four for women over 50, men over 70, or adolescents.

Try to meet your targets with food first, and use supplements to fill the gaps. Bone meal from a lead-tested product is the best by default. Calcium citrate is best for those who need to avoid phosphorus or collagen, or who are at high-risk of kidney stones.

Phosphorus deficiency is mainly a risk of mostly fat diets, starvation, anorexia, or eating disorders.

Keto carnivore is at the greatest risk of deficiency but can avoid it with enough dairy, eggs, or meat. Regular keto can use veggies too.

Phosphorus levels drop in refeeding syndrome or hungry bone syndrome. Meat and eggs are great for refeeding and dairy is great for hungry bone.

We can avoid getting too much phosphorus by avoiding processed foods.

Remember that vitamin D requirements go down when you get enough calcium and go up when you get too much phosphorus. Before concluding you need more D than recommended in the lessons, check your calcium/phosphorus balance.