I have this conversation with patients fairly often.
When we're reviewing lab results, someone will point out that their calcium level is normal, so at least they know they're getting enough calcium.
It's a completely reasonable assumption. It's just not what a blood calcium level is telling us.
A normal calcium level tells us that the symphony of physiology keeping your calcium tightly regulated (your kidneys, parathyroid hormone, vitamin D, and gut) is doing its job beautifully. And that's great!
What it doesn't tell me is whether your body is having to pull calcium from your bones to maintain that harmony.
So my next question is usually: about how much calcium do you typically get from food and supplements most days?
And I get it. None of us want to track nutrient intake. But it's pretty darn hard for me to tell you whether you're getting enough without at least a few days of tracking.
In this article, I'll walk through what that normal number really means, how much calcium you actually need (the research may surprise you), a simple way to estimate your intake, and how I think about supplements, including why I prefer one form over the others.
What does your blood calcium actually tell you?
Your blood calcium is one of the most tightly controlled numbers in your body. It has to be. Calcium is essential for your heart rhythm, nerve signaling, and muscle contraction, so your body can't let it drift much in either direction.
Several systems work together to keep it steady: your parathyroid glands, vitamin D, your gut, your kidneys, and your bones.
When calcium intake is low, your parathyroid glands release more parathyroid hormone (PTH). PTH signals your kidneys to hold on to more calcium and to produce more active vitamin D, which increases how much calcium your gut absorbs. And if that isn't enough, it pulls calcium out of the biggest calcium reserve you have, your bones.
In other words, a normal blood calcium doesn't exclude the possibility that some of your calcium is coming from your bones.
And waiting for a DEXA scan to tell us there's a problem, isn't the proactive approach I prefer to take. (Since you're spending your time reading this, I'm guessing it's not your preference either.)
How much calcium is enough?
This is where the evidence is less clear.
In the United States, recommended calcium intake for adults generally ranges from 1,000 to 1,200 mg daily, depending on age and sex. In the United Kingdom, the 2024 osteoporosis guideline recommends considerably less, a minimum of 700 mg daily.
And importantly, research hasn't consistently shown that people who consume more calcium keep higher bone density or lose bone more slowly. In one study of 570 healthy postmenopausal women, calcium intake had no relationship to bone loss over five years, despite big differences in how much they ate. A 2021 review of long-term studies found the same pattern, most showed no link between calcium intake and changes in bone density, especially in women over 60.
But calcium does still matter. Bone is built from it.
If you're building a brick house, you can have the best bricklayers in town, but if they don't have any bricks, you just aren't going to get very far. And when intake is truly low, your body draws on your skeleton to keep blood levels normal. But above a somewhat modest level, one many people can reach through food alone, more calcium doesn't appear to mean stronger bones. Once there are enough bricks on site, extra bricks just sit in the pile. At that point, it's the bricklayers who determine how much gets built.
So these recommendations are useful reference points, not precise thresholds below which your bones are necessarily losing calcium, or above which they're protected.
Nerd Note: Why Doesn't More Calcium Mean More Bone?
Partly because your body adapts. When intake drops, your gut absorbs a larger percentage of what you eat and your kidneys excrete less. That buffer works well across a wide range, until intake gets low enough that it can't keep up.
The other reason is that bone is always remodeling. Cells called osteoclasts constantly break down old bone, while osteoblasts build new bone to replace it.
Whether your bones come out stronger or weaker depends in large part on the signals those cells receive: hormones like estrogen, mechanical loading from strength training, and nutrition.
After menopause, falling estrogen ramps up osteoclast activity, so breakdown typically starts to outpace building.
Extra calcium can't fix a signaling problem. In our analogy, these signals are what direct the bricklayers.
My approach is to find out how much calcium someone is actually getting, then look at the bigger picture: their bone density, fracture risk, menopause status, and whether they're on an osteoporosis medication, which makes adequate calcium more important. From there, we decide whether more dietary calcium or a supplement makes sense.
How do you find out what you're getting?
You track it. And I know, this is no one's favorite task.
But realistically, it's the only way to know where you stand. There's no blood test for calcium intake.
The good news is that you don't need to track forever. The goal isn't perfection. It's a realistic picture of where you are, so we can decide whether you need more. For most adults, I'd want to see at least 700 mg a day. For postmenopausal women with low bone density, or anyone on an osteoporosis medication, I generally aim higher, somewhere between 800 and 1,200 mg, depending on the specific clinical situation. A rough estimate is enough to tell where you fall.
Here are two ways to do it:
The 3-day snapshot. Log everything you eat for three typical days, including one weekend day, in an app like Cronometer. Add any calcium from supplements, including multivitamins and antacids like Tums. Then average the three days.
The quick estimate. If you don't want to log, start with about 300 mg for the calcium scattered through a typical diet. Then add roughly 300 mg for each serving of a calcium-rich food like the ones below.
Some common sources (amounts are approximate, so check labels when you can):
| Food | Serving | Calcium (mg) |
|---|---|---|
| Plain yogurt or kefir (cow, goat, or sheep) | 1 cup | 300–400 |
| Milk (cow or goat) | 1 cup | about 300 |
| Hard cheese | 1.5 oz | 300–330 |
| Canned sardines, with bones | 1 can (3.75 oz) | about 350 |
| Tofu made with calcium sulfate | ½ cup | 250–430 |
| Collard greens, cooked | 1 cup | about 270 |
| Canned salmon, with bones | 3 oz | about 180 |
| Kale, cooked | 1 cup | about 180 |
| Almonds | 1 oz | about 75 |
You'll notice spinach isn't on the list. It's high in calcium on paper, but it also contains oxalate, which binds calcium and blocks most of it from being absorbed.
Food first, then fill the gap
If your estimate comes in comfortably above your target, you may not need a calcium supplement at all. That makes it easy.
If you're below, consider food options first. Is there a calcium rich food you'd genuinely enjoy adding to your day? Supplements are meant to be just that: supplemental. That said, for people who don't do well with dairy, getting enough calcium from food most days can be harder.
If food alone won't get you there, a supplement can fill the gap. A few practical points:
Keep doses to 500 mg or less at a time. Your gut absorbs smaller doses more efficiently. If you need more, split it across meals.
Take it with food. This also spreads out its effect on your blood calcium.
Watch the timing with iron. Calcium can reduce iron absorption. If your iron tends to run low, take your calcium supplement at a different time from iron supplements or iron-rich meals.
Count everything. Multivitamins, "bone support" blends, and antacids all add up.
Why are calcium supplements controversial?
About 15 years ago, analyses of randomized trials suggested that calcium supplements might modestly increase the risk of heart attack. Not everyone agrees with those findings, and the debate is ongoing. But they raised a real question: why would calcium from a pill behave differently than calcium from food?
One leading explanation has to do with your blood calcium.
When you eat calcium in food, it comes in smaller amounts, mixed with other nutrients, spread throughout the day. Your blood calcium barely moves.
With common calcium supplements, like calcium carbonate or citrate, your blood calcium rises noticeably and can remain elevated for hours.
One concern is that repeated increases in circulating calcium might influence blood clotting or vascular calcification over time. Whether these changes actually explain the cardiovascular risks reported in some studies remains uncertain.
Still, it's the reason I care about which form of calcium someone takes, and why I'd rather fill a small gap than supplement the whole target.
If You Need a Supplement, Does the Form Matter?
When someone does need a supplement, my preferred form is microcrystalline hydroxyapatite (MCHA). It's made from bone, often from pasture-raised cattle, and it contains calcium and phosphorus in the same mineral form found in your own skeleton, along with small amounts of bone proteins and trace minerals.
There's something intuitive about getting calcium from bone. For most of human history, people who ate animals used the whole animal, including bone: cracking bones for marrow, chewing the softer ends, and eating small fish bones. But "ancestral" isn't my main reason. Here's what the research shows:
A gentler rise in blood calcium. In a randomized trial of 100 postmenopausal women, MCHA raised blood calcium less than calcium citrate or carbonate.
The same effect on bone turnover. In that same trial, MCHA lowered markers of bone breakdown and turnover just as much as the conventional supplements did. So a smaller blood calcium spike didn't seem to mean less benefit for bone.
Possibly better bone density. A 2009 analysis of six trials found that a related bone-derived form (ossein-hydroxyapatite) preserved about 1% more bone density than calcium carbonate.
Nerd Note: What Does the Research Show?
Most of the research shows bone-derived calcium slowing bone loss rather than building new bone.
In a large three-year observational study of perimenopausal women, spine bone density stayed stable with the bone-derived form but fell about 3% with calcium carbonate.
In a smaller randomized trial of older women with osteoporosis, spine density dipped with both, but less with the bone-derived form (about −1% vs. −2%), while hip density rose slightly in both groups (about +2.5% vs. +1.2%).
Neither study was blinded. But they compared bone-derived calcium to another calcium supplement, which is a stronger design than the AlgaeCal studies below, which had no comparison group and reported bigger gains.
To be fair, there are caveats:
The bone density studies were small, several weren't blinded, and some had industry funding. None looked at fractures, which is what we really care about.
No study has shown that MCHA actually lowers cardiovascular risk. The logic is reasonable, but it hasn't been tested.
Because it comes from bone, quality matters. I look for brands that test for heavy metals and source from cattle in countries with no history of mad cow disease, such as New Zealand.
So MCHA isn't magic. But given its comparable effects on bone turnover and smaller rise in circulating calcium, it's my preferred form when supplementation makes sense. Whether those differences translate into better long-term bone or cardiovascular outcomes remains to be established.
What about AlgaeCal?
Because the question of whether AlgaeCal is the "best" calcium supplement for bone comes up fairly often, I wanted to share my thoughts. (If AlgaeCal has never crossed your mind, feel free to skip ahead.)
AlgaeCal is a calcium supplement made from a South American red algae, often sold with a separate product called Strontium Boost.
There are three main human studies, all funded by the company. (That doesn't mean I toss out the results, but it does make me look more closely at how a study was designed and what it actually measured.) Two things stand out:
There was no real comparison group. Instead of comparing AlgaeCal to a placebo or another calcium supplement, the studies compared results to the bone loss researchers expected for people that age.
The biggest gains came with added strontium. Most participants also took strontium, along with extra vitamins, minerals, and in some cases an exercise program. The one group that took the algae calcium without strontium saw a more modest increase, about 1% per year, in a small group of 35 women.
Here's why the addition of strontium to these studies complicates matters.
Strontium is a heavier element than calcium. When it's built into bone, it makes bone look denser on a DEXA scan than it really is. So when someone taking strontium sees their bone density jump, we can't tell how much of that is new bone and how much is the scan reading the strontium. And a higher number on a DEXA scan, especially with strontium on board, doesn't necessarily mean stronger or more fracture-resistant bones.
There's also a safety question. The prescription form of strontium, sold in Europe, did reduce fractures, but it also increased the risk of heart attack and blood clots, and its use is now heavily restricted. Strontium citrate, the form in supplements, hasn't been studied for either.
On top of that, the studies measured total body bone density rather than the spine and hip (as done on typical DEXA bone density scans), and none looked at fractures.
My take: the strontium-free results are encouraging, but they don't show that algae calcium is better than any other form. That said, for vegetarians, who prefer to avoid a bone-derived form like MCHA, an algae-based calcium (without the strontium) would probably be my preferred choice.
The bottom line
A normal calcium level is reassuring, but it doesn't tell us how much calcium you're consuming, or how much your bones actually need.
Estimating your intake is a useful starting point. From there, we can consider your overall bone health, prioritize food sources, and decide whether supplementation makes sense.
So where does that leave calcium supplements? I still believe there's a floor, and it matters most for people who don't include much dairy, beyond a splash of milk in their coffee. But if I had to pick one intervention to improve bone health, it would be resistance training with relatively heavy loads. Because bone is a living, responsive tissue, not simply a calcium storage container. But strength training works best when you're getting enough calcium to build with.
For those of us at higher risk of osteoporotic fractures, ensuring adequate calcium intake remains an important part of the picture. Whether supplements offer additional benefit depends on how much calcium we're already consuming, our overall bone health, and our individual risk factors.
And remember, calcium is only one piece of the picture. Strong bones depend on much more than a single nutrient, or a single number on a lab report.
