What Are the Signs of Low Calcium? Intake, Blood Levels and Tests

Low calcium means two different things, and only one of them has signs you can feel. A low calcium intake has no symptoms for years, because the body holds blood calcium steady by drawing on bone; a diet short of calcium shows up as lower bone density and a higher fracture risk on a scan, not as anything you notice. A low blood calcium, hypocalcaemia, is a medical condition with tingling around the mouth and in the fingertips, cramps and muscle spasms, and it is almost never caused by diet: the usual causes are the parathyroid glands, vitamin D deficiency, kidney disease, low magnesium and some medicines.^{1, 2} The "10 signs of low calcium" lists online fuse the two, then add brittle nails, dry skin and thinning hair, which are not calcium signs.³ What to check instead: your intake against the UK's 700 mg a day, your vitamin D, and, if you have the tingling and cramps, a GP blood test.

• Low intake: silent; shows on a bone density scan years later; count your food against 700 mg
• Low blood calcium: tingling, cramps, spasms; a GP blood test; causes other than diet
• Not calcium signs: brittle nails, dry skin, thinning hair, tiredness on its own, "brain fog"
• Raising a low intake: food first, a supplement for the gap, and vitamin D so the calcium is absorbed

Low calcium intake vs low blood calcium: the difference

Blood calcium is one of the most tightly controlled numbers in the body, held between about 2.2 and 2.6 mmol/L by the parathyroid glands, vitamin D and the kidneys. If you eat too little calcium, the parathyroid glands release more hormone, the kidneys hold on to calcium, and bone gives up some of its mineral to keep the blood level normal. The blood test stays normal; the bone pays. Over years that shows as lower bone density, the band a scan calls osteopenia (what is osteopenia explains it), and a higher fracture risk, and the first "symptom" of a low intake can be a wrist fracture from a fall that should not have broken anything.⁴ Hypocalcaemia is the opposite situation: the control system itself has failed, blood calcium has dropped below the normal range, and nerves and muscles start to misfire. Diet is almost never the cause, because the bone reservoir is so large. This is why there is no blood test for calcium intake and no symptom checklist for it either; the only way to know your intake is to count it.

Symptoms of hypocalcaemia

Low blood calcium makes nerves more excitable, so the early signs are sensory and muscular: tingling or numbness around the mouth and in the fingers and toes, muscle cramps, twitching, and spasms of the hands and feet in which the fingers draw together.¹ Doctors test for two classic signs: twitching of the face when the cheek is tapped (Chvostek's sign) and a hand spasm when a blood pressure cuff is inflated for a few minutes (Trousseau's sign). Severe or sudden hypocalcaemia can cause prolonged spasms, seizures, breathing difficulty from spasm of the voice box, and heart rhythm changes, and it is treated in hospital. Long-standing mild hypocalcaemia can be vaguer, with tiredness, low mood and dry skin, but alongside the tingling and a low blood result, not as stand-alone signs of a diet short of calcium.^{1, 2} If you have tingling around the mouth and cramps that keep coming back, see your GP; if you have spasms you cannot release, trouble breathing or a seizure, that is an emergency.

What causes low blood calcium?

Most cases trace to the parathyroid glands or vitamin D. Hypoparathyroidism, when the glands make too little hormone, usually follows thyroid or neck surgery and sometimes an autoimmune condition.² Severe vitamin D deficiency lowers calcium absorption enough to tip blood levels down, and in children it is the cause of rickets. Chronic kidney disease, low magnesium (which stops the parathyroid glands working properly), acute pancreatitis and some medicines, including certain osteoporosis treatments, anti-epileptics and loop diuretics, can all lower blood calcium.¹ A blood test corrected for albumin, with vitamin D, magnesium, kidney function and parathyroid hormone measured alongside, finds the cause; treatment is of the cause, under a doctor, and a food supplement is not the treatment for hypocalcaemia.

Signs that are not calcium

Brittle or ridged nails do not reflect calcium intake. Nails are keratin, and a review of nutrition and nail disease found no evidence that calcium affects nail strength; brittle nails track dryness, water exposure, iron deficiency and thyroid problems far more often.³ Dry skin, thinning hair, "brain fog" and tiredness on their own have dozens of causes and no study links any of them to a low calcium intake in otherwise healthy adults. Night-time muscle cramps are usually not calcium either; they are common, mostly unexplained and more often linked to medicines or dehydration than to diet. If a list offers ten signs of calcium deficiency, it is describing hypocalcaemia and padding it out.

How do I tell if my calcium levels are low?

Two different checks for the two different things. For intake, add up a typical day in UK portions: a 200 ml glass of milk or fortified plant milk about 240 mg, a 150 g pot of yoghurt about 240 mg, 30 g of hard cheese about 220 mg, 100 g of calcium-set tofu about 350 mg, 100 g of tinned sardines with bones about 400 mg, two slices of UK bread about 120 mg.⁵ Under 700 mg on most days means your intake is low, whatever a blood test says. For blood calcium, only a GP blood test will do; home finger-prick kits that report "calcium" are measuring the same tightly controlled number and will read normal in almost everyone who eats too little. Foods high in calcium has the full UK portion list.

What organ is affected by low calcium?

The parathyroid glands regulate it, bone stores it, the kidneys and gut adjust it, and nerves and muscles are where a low blood level shows. Four pea-sized glands behind the thyroid sense blood calcium minute by minute and release parathyroid hormone when it dips, which pulls calcium from bone, tells the kidneys to keep it and switches on the active form of vitamin D so the gut absorbs more.² A low intake therefore affects bone first and only. A low blood level affects the nervous system and muscles, including the heart, which is why severe hypocalcaemia is treated urgently. The thyroid gland, which sits in front of the parathyroids and is often confused with them, has no direct role in calcium control.

Who is at risk of a low calcium intake?

People who avoid dairy without fortified plant milks, calcium-set tofu or tinned fish with bones; teenage girls and women on the low intakes the National Diet and Nutrition Survey keeps finding; older adults eating smaller meals, especially in care; and anyone on a long-term restricted diet.⁶ Add vitamin D deficiency to the risk, because calcium absorption depends on it and the NHS advises everyone to consider 10 micrograms a day in autumn and winter.⁷

How to raise a low calcium intake

Food first, because food calcium comes with protein and the other minerals bone also needs, and it raises bone density by the same one to two per cent in a year as a supplement does.⁴ A glass of milk or fortified plant milk, a pot of yoghurt and a matchbox of cheese cover most of 700 mg; a tin of sardines, calcium-set tofu, kale and almonds carry a dairy-free day. Where the count still falls short, a supplement sized to the gap closes it, and 500 mg or less at a time is absorbed best. Calcium is needed for the maintenance of normal bones and teeth, and vitamin D contributes to the normal absorption and utilisation of calcium. Do you need a calcium supplement covers who the gap applies to, the heart question and how to take one; can you rebuild bone density sets out why loading exercise moves bone density more than any nutrient, and the Wellgard joint health guide covers the joints.

Frequently asked questions

How do you feel when your calcium is low?

If your intake is low, you feel nothing; bone absorbs the shortfall silently. If your blood calcium is low, you feel tingling around the mouth and in the fingertips, muscle cramps and twitching, and in severe cases spasms, which needs a GP blood test.¹

What are two signs of low calcium?

The two classic signs doctors look for in hypocalcaemia are Chvostek's sign, a facial twitch when the cheek is tapped, and Trousseau's sign, a hand spasm when a blood pressure cuff is inflated. The two everyday signs are tingling around the mouth and muscle cramps.¹

What drains calcium from your body?

A high salt intake raises the calcium lost in urine, vitamin D deficiency stops it being absorbed, and long-term steroid medicines, heavy alcohol and some acid-suppressing medicines work against it.⁸ None of these drains the blood level; they widen the gap bone has to cover.

Which fruit is highest in calcium?

Dried figs, at about 75 mg in a 30 g portion, then oranges at about 60 mg each; no fruit is a major source, and a glass of milk or fortified plant milk carries more than any of them.⁵

What happens if calcium is too low?

In the blood: tingling, cramps and spasms, then seizures and heart rhythm changes if it falls far or fast, which is why hypocalcaemia is treated in hospital and its cause corrected under a doctor.¹ In the diet: nothing you feel, then lower bone density and a higher fracture risk over years.⁴

Sources

1. Cooper MS, Gittoes NJ. Diagnosis and management of hypocalcaemia. BMJ, 2008. PubMed 18535072.
2. NHS. Hypoparathyroidism. nhs.uk.
3. Cashman MW, Sloan SB. Nutrition and nail disease. Clinics in Dermatology, 2010. PubMed 20620759.
4. Tai V, et al. Calcium intake and bone mineral density: systematic review and meta-analysis. BMJ, 2015. PubMed 26420598; Bolland MJ, et al. Calcium intake and risk of fracture: systematic review. BMJ, 2015. PubMed 26420387.
5. Public Health England. McCance and Widdowson's The Composition of Foods Integrated Dataset. gov.uk; NHS. Calcium: vitamins and minerals. nhs.uk.
6. Public Health England and the Food Standards Agency. National Diet and Nutrition Survey. gov.uk.
7. NHS. Vitamin D: vitamins and minerals. nhs.uk.
8. Heaney RP. Role of dietary sodium in osteoporosis. Journal of the American College of Nutrition, 2006. PubMed 16772639.

This article is general information, not medical advice. Tingling around the mouth, cramps and spasms that keep returning need a GP blood test; spasms you cannot release, difficulty breathing or a seizure need emergency care.