Calcium Deficiency: Symptoms, Tests, Intake, Foods

Calcium supports bone strength, muscle contraction, nerve transmission, and coagulation. Two realities intersect: insufficient dietary intake (common) and hypocalcemia (low blood calcium), which is rarely due to intake alone because blood calcium is tightly regulated. In practice, we look for clinical signs, assess intake, check vitamin D and PTH, and evaluate long-term bone risk. Key references: recommended intakes (NIH ODS) and EFSA dietary reference values.

Symptoms (low intake → bone risk; hypocalcemia)

Cramps, spasms, paresthesia (hypocalcemia); Chvostek/Trousseau signs if severe
Muscle fatigue, stiffness, pain
Brittle nails, dental caries and dental problems
Fragile bones with osteoporosis risk and fractures long-term if chronically low intake
Risk factors: very low dairy intake, veganism without fortified foods, malabsorption, post-menopause, adolescence, low vitamin D exposure

For the clinical picture and causes of hypocalcemia, see the hypocalcemia fact sheet (MSD, EN).

Important distinction

A normal blood calcium does not rule out insufficient dietary intake: PTH compensates via bone. Bone risk remains possible despite "normal" blood calcium.

Tests and markers

Albumin-corrected total calcium or ionized calcium: confirm hypocalcemia (if present).
25-hydroxy-vitamin D: low status reduces intestinal calcium absorption.
PTH: elevated if hypocalcemia secondary to low intake/vitamin D, low in hypoparathyroidism.
Phosphorus, creatinine: renal/mineral workup.
Bone densitometry (DXA): useful to assess bone risk if risk factors present.

For interpretation and marker limitations, see the NIH ODS – Calcium fact sheet.

Calcium-rich foods (and bioavailability)

Dairy products (milk, yogurt, cheese): high content and favorable bioavailability
Fish with edible bones (canned sardines)
Calcium-rich mineral waters (e.g., > 400 mg/L): useful lactose-free source
Green vegetables (kale, broccoli), almonds, sesame seeds (tahini), calcium-set tofu
Fortified foods (plant-based drinks, cereals)

Oxalates (spinach) and phytates (some grains/legumes) can reduce absorption. For precise values, consult USDA FoodData Central.

Dosage and tolerance

Target intake (adults)

NIH ODS (RDA): 1,000 mg/day (men 19–70, women 19–50), 1,200 mg/day (men ≥ 71, women ≥ 51) — see detailed recommendations.
EFSA (PRI): ~950 mg/day in adults (reference value), summary EFSA DRV.

Upper limit (UL)

UL: 2,500 mg/day (adults) in several frameworks; some age groups have UL 2,000 mg/day — see NIH ODS.
Kidney stone risk: especially with high supplement doses in predisposed individuals.
Interactions: calcium can decrease absorption of iron, zinc, tetracyclines/fluoroquinolones — space doses (see ODS interactions).

Practical advice

Prioritize food sources first. If needed, split supplements (e.g., 300–500 mg with meals) for tolerance and absorption. Ensure adequate vitamin D if status is low.

FAQ

Does blood calcium tell me if I'm getting enough dietary calcium?
Not necessarily. Blood calcium is regulated. We assess intake, vitamin D, PTH, and bone context.

Calcium carbonate vs. citrate?
Citrate is better tolerated by some and less dependent on stomach acid; carbonate is more concentrated in elemental calcium. Choose based on tolerance/meals.

Can mineral waters help?
Yes, calcium-rich waters provide 100–600 mg/L depending on brand — practical if lactose-free.

Who is most at risk?
Post-menopause, adolescents, dairy-free diets, malabsorption, low vitamin D status.