Worried About Calcium? How to Optimise Absorption and Protect Your Bones

Most people think of calcium just as a “bone mineral”. But even if 99% of it is tucked safely into your bones and teeth, the remaining 1% — the tiny fraction circulating in your blood and cells — is what keeps you alive. That 1% powers muscle contraction (including your heartbeat), nerve signalling, blood clotting, hormone release, and enzyme activation.

These are non‑negotiable metabolic duties, and your body will always prioritise them over bone density. So when blood calcium dips even slightly — or when your diet pushes your blood chemistry toward acidity — your body pulls calcium out of your bones to restore balance. You can be eating “enough” calcium on paper and still be on overdraft.

Your body maintains blood pH in a razor‑thin range. When your diet leans heavily toward sugar, ultra‑processed foods, refined grains, excess sodium, chronic stress (yes, it counts)… it creates a more acid‑forming metabolic load.

To buffer this and keep blood pH stable, your body uses alkaline minerals — including calcium. If your diet doesn’t supply enough, your body withdraws calcium from your bones to maintain homeostasis.

How to optimise calcium intake from food

The RDI for calcium is based on total intake, not what you actually absorb. The assumption is that humans absorb only 25–35% of dietary calcium on average. So the recommended 1000–1200 mg/day is set high enough to ensure that the absorbed amount meets physiological needs.

The amount of calcium your body actually absorbs depends not only on the food source but also on how you combine it and the state of your gut.

• Bioavailability of calcium is enhanced in the presence of vitamin D, lactose, casein phosphopeptides (in cheese/yogurt) and is better absorbed in the presence of adequate stomach acid.

• It is inhibited by oxalates (present in spinach, chard, beet greens, sesame), phytates (nuts, seeds, whole grains), excess fibre, low stomach acid, and gut inflammation.

To give you an idea of bioavailability of calcium in foods, this table shows the approximate amount of absorbable calcium per serving:

Food	Total Ca	Estimated  Absorption	Approx. Absorbable Ca
100 g canned sardines (with bones)	~380 mg	30%	~120mg
1 cup cooked kale	~180 mg	50%	~90 mg
1 cup (200ml) full‑fat milk	~250 mg	30%	~75 mg
Fortified plant milk replacement	~240mg	30%	~72 mg
1 cup cooked broccoli	~60 mg	50%	~40 mg
½ cup *120g) full‑fat Greek yogurt	~100 mg	30%	~30 mg
1 tbsp un-hulled tahini	~120 mg	20%	~25 mg
1 tbsp Parmesan	~55 mg	30%	~15 mg
1 tbsp hulled tahini	~ 65 mg	20%	~13 mg
1 cup bone broth (depending on prep)	~20-40 mg	30%	~10 mg
100g fresh figs	~ 30 mg	30%	~10 mg

PRO TIP: Iron and calcium compete for absorption; if you need to optimise your intake try having a calcium rich breakfast or lunch and an iron rich dinner, avoiding combinations such as red meat and cheese or lentils and cream.

Bone health is not just about calcium

• Support the D3–K2–Magnesium trio

Vitamin D3 boosts calcium absorption, magnesium activates D3 into its usable form, and vitamin K2 directs calcium into bones instead of soft tissues.

• Eat protein consistently

Adequate intake improves bone density and reduces fracture risk.

• Reduce inflammation

Through whole foods, omega‑3s, gut health, and blood sugar balance.

• Lift heavy things

resistance training and impact exercise stimulate osteoblast activity and increase bone mineral density.

• Limit bone‑draining habits

Excessive caffeine, alcohol, sugar and UPFs, low calcium intake, smoking, stress.

• Mind the gut

Dysbiosis and low stomach acid reduce mineral absorption; fermented foods and digestive support help

Final thoughts...

Most people eating a varied, whole‑foods diet don’t need calcium supplements. Because calcium is tightly regulated in the body, excess from supplements can end up where you don’t want it: kidneys, arteries, and soft tissues rather than your bones. It can also interfere with medications and disrupt the balance of other key nutrients. Unless a qualified practitioner has identified a genuine need and prescribed the right form, dose, and timing,  sticking to food sources is almost always the safer, smarter choice.