Calciummmol/L
Calcium regulation
Also known as: Total Calcium
Typical optimal range
2.2–2.6 mmol/L
A typical optimal range for serum calcium is 2.2–2.6 mmol/L, though exact reference intervals vary between laboratories and their analysers, so always interpret your result against the range printed on your own report. These figures are indicative — the range printed on your own lab report is the definitive one for your results.
Interpretation of serum calcium follows NHS and laboratory medicine guidance; NICE provides clinical guidance on the investigation and management of hypercalcaemia and hypocalcaemia as part of broader endocrine and metabolic pathways.
What is Calcium?
Serum calcium measures the total amount of calcium circulating in your blood, including the portion bound to proteins (mainly albumin) and the smaller, biologically active free fraction. Calcium is essential for bone strength, muscle contraction, nerve signalling, and heart rhythm. Because the body regulates blood calcium very tightly through parathyroid hormone (PTH) and vitamin D, a result outside the normal range usually reflects a problem with that hormonal control system rather than simply what you have eaten. Measuring it is useful because both persistently high and persistently low levels can have significant health consequences that are often treatable once identified.
What a high Calcium means
A raised serum calcium — known clinically as hypercalcaemia — is a signal that the body's tight regulatory system may be under strain and warrants further investigation, but a single elevated result does not mean something serious is wrong. Your GP will want to repeat the test and look at other markers to understand what is driving it.
- Primary hyperparathyroidism. The most common cause of persistent mild hypercalcaemia in otherwise well adults. The parathyroid glands produce too much PTH, which raises calcium by increasing bone resorption and kidney reabsorption. It is often detected incidentally on a routine blood test and is frequently manageable.
- Malignancy. Some cancers — including lung, breast, and myeloma — can raise calcium either by spreading to bone or by secreting PTH-related protein. This is a less common cause overall but is important to rule out, especially if calcium is significantly raised or accompanied by other symptoms.
- Excess vitamin D or supplements. Very high doses of vitamin D supplements can cause calcium to rise by increasing intestinal absorption. This is uncommon at the doses recommended for most people in the UK, but is worth flagging if you take high-dose supplements.
Calcium results can be affected by dehydration and by the albumin level — a high albumin (e.g. after a tourniquet is left on too long during blood draw) can make calcium appear falsely elevated. Many labs automatically report an albumin-adjusted or 'corrected' calcium figure, which is more reliable.
What a low Calcium means
A low serum calcium (hypocalcaemia) can reflect a genuine deficiency in the regulatory system, but one of the most common reasons for a low result is a low albumin level rather than true calcium deficiency — which is why the corrected calcium figure is so important. True hypocalcaemia does warrant further assessment.
- Vitamin D deficiency. Vitamin D is essential for calcium absorption from the gut. Deficiency — which is common in the UK, particularly in winter months and among people with darker skin or limited sun exposure — can lead to reduced calcium levels and is a frequent, treatable cause.
- Hypoparathyroidism or kidney disease. Underactive parathyroid glands (sometimes after neck surgery) or chronic kidney disease reduce the body's ability to regulate calcium, leading to persistently low levels that usually need specialist management.
A low calcium result should always be interpreted alongside albumin; if albumin is low, the corrected calcium may actually be normal. Your lab report will usually show both figures.
Should I be worried?
A single calcium result slightly outside the reference range is not a reason to panic — results can vary day to day and are influenced by factors like dehydration, albumin levels, and even how the blood sample was taken. What matters is the pattern over time. If your calcium is flagged as high or low, your GP will typically arrange a repeat test and may check related markers such as PTH, vitamin D, albumin, kidney function, and phosphate to build a full picture. Symptoms such as fatigue, muscle cramps, excessive thirst, or confusion alongside an abnormal result are worth mentioning promptly, but many people with mildly abnormal calcium levels feel entirely well and the cause turns out to be straightforward. Use this result as a starting point for a conversation with your GP rather than a cause for concern.
What actually helps
Because serum calcium is hormonally regulated, the most evidence-based lifestyle levers focus on supporting the vitamin D and parathyroid system rather than simply eating more calcium-rich foods.
- Maintain adequate vitamin D. Vitamin D is the key driver of calcium absorption in the gut. Public Health England recommends that everyone in the UK consider a daily supplement of 10 micrograms (400 IU) of vitamin D, especially during autumn and winter. People at higher risk of deficiency may need a higher dose under medical supervision.
- Balanced dietary calcium intake. An intake of around 700–1000 mg of calcium per day from food is a broadly recommended target for most adults in the UK. Getting this from a varied diet rather than high-dose supplements is generally preferred, as excessive supplemental calcium has been associated with a small increased risk of kidney stones in some studies.
- Limit very high-dose vitamin D or calcium supplements without guidance. Over-supplementing with vitamin D or calcium can push serum calcium upward. If you take supplements, stick to recommended doses unless a clinician has advised otherwise, and mention all supplements to your GP when discussing your results.
- Support kidney health. The kidneys play a central role in calcium balance. Staying well hydrated and managing conditions like hypertension and diabetes — which can affect kidney function — indirectly supports calcium regulation over the long term.
There is good supporting evidence for a calcium-rich, varied diet as the foundation for healthy calcium balance.
Dairy (milk, yogurt, cheese)
Among the richest and most bioavailable dietary sources of calcium; a standard 200 ml glass of milk provides roughly 240 mg of calcium.
Fortified plant milks (soya, oat, almond)
UK-sold fortified plant milks are typically calcium-fortified to levels similar to cow's milk, making them a reliable alternative for those who avoid dairy.
Tinned fish with bones (sardines, salmon)
The soft, edible bones in tinned sardines and salmon are a useful source of calcium that is widely available and affordable in the UK.
Green leafy vegetables (kale, spring greens, broccoli)
These contain meaningful amounts of calcium in a form that is reasonably well absorbed; note that spinach is high in calcium on paper but has lower bioavailability due to oxalate content.
Fortified breakfast cereals
Many standard UK cereals are fortified with calcium and can contribute meaningfully to daily intake, particularly at breakfast.
Nuts and seeds (almonds, sesame/tahini)
Almonds and sesame seeds (including tahini) provide a useful plant-based calcium contribution alongside other beneficial nutrients.
Track your own Calcium
Upload a lab PDF and Better Days trends Calcium over time, flags it when it drifts, and suggests foods that help.
More in Vitamins/Minerals
Sources & further reading
These are reputable UK health resources for further reading. This page is written to be consistent with their guidance but is not a substitute for them.
For information only — not medical advice, and not individually reviewed by a clinician. Reference ranges vary by lab and individual. Discuss any results with a qualified clinician before making changes.