Calcium is the most abundant mineral in the body, yet few experts agree on what its normal blood levels should be. Read on to understand if your calcium test results are suboptimal, based on the latest research and factors labs rarely take into account.

Calcium Blood Test

Let’s first brush up on the basics. You probably got your calcium blood test results back or are planning to undergo testing soon.

A calcium test measures your calcium levels in the blood. Most commonly, the test estimates your total serum calcium levels and includes [1, 2]:

  • Calcium bound to proteins, mainly albumin (about 40%)
  • Calcium complexed with phosphate and citrate (about 10%)
  • Ionized calcium, also known as free or active calcium (about 50%)

You don’t need to prepare for this test or fast beforehand. A healthcare professional will simply collect a blood sample from your vein that will be analyzed.

The calcium blood test is often done as part of a routine metabolic panel. The basic metabolic panel (BMP) checks blood sugar, calcium, and electrolytes, as well as kidney function. The comprehensive metabolic panel (CMP) also includes cholesterol, protein levels, and markers of liver function [3].

Your doctor may also order an ionized (free) calcium test.

Ionized calcium is the body’s active form of calcium. It is assumed to be around 50% of the total blood calcium, although the exact percentage may vary. Ionized calcium levels are often just estimated based on total blood calcium and albumin levels. Testing ionized calcium is far more precise, but it requires special equipment and is expensive [1].

Factors Affecting Normal Calcium Levels

The normal ranges for calcium levels in adults are 8.5 to 10.5 mg/dL. These values can vary slightly can lab to lab, sometimes even up to 0.5 mg/dL [4, 5].

However, labs determine a normal range that applies to all people – regardless of their age, gender, and health status.

Gender and Age

Calcium levels may vary slightly in men and women. The normal range also slightly shifts with aging. In men over 69 years, calcium dropped from a mean of 9.6 mg/dL to 9.4 mg/dL, according to one study. In women, the mean increased from 9.6 mg/dL to 9.8 mg/dL for those over 50 years old [6].

According to a different study, calcium levels only slightly drop with aging in men, while they tend to remain stable in women. The inconsistency could be due to the number of people analyzed and how scientists define a “significant change” or “stable levels” [7].

Infants and children have higher calcium levels than adults. Below are data from a review study that shows the variations in calcium levels according to gender and age [7]:

AgeTotal blood calcium (mg/dl)
Newborns0-4 months8.8-11.3
Babies1-5 years9.4-10.8
Children6-12 years9.4-10.3
Men20 years9.1-10.2
50 years8.9-10.0
70 years8.8-9.9
Women20 years8.8-10.0
50 years8.8-10.0
70 years8.8-10.0


Hypocalcemia
(“hypo” = low, “calcemia” = calcium in the blood) is when calcium blood levels drop below 8.5 mg/dL. You can read more about the symptoms and causes of hypocalcemia in our posts on calcium deficiency.

Hypercalcemia (“hyper” = high, “calcemia” = calcium in the blood) is when calcium blood levels rise above 10.5 mg/dL. We detail all the causes of high blood calcium here. However, one cause often goes unnoticed, especially in older people: hyperparathyroidism.

Minerals and Hormones

Calcium blood levels depend on several important factors, including [5]:

  • Parathyroid hormone (PTH)
  • Vitamin D
  • Phosphorous
  • Magnesium

PTH

Calcium blood levels are mainly controlled by parathyroid hormone (PTH). Cells in your parathyroid gland – located in the neck just behind the thyroid – release PTH when they sense a drop in calcium blood levels [8].

PTH raises blood calcium levels by increasing the absorption of calcium from the gut and kidneys. This hormone also mobilizes calcium and phosphate from the bones: that is, it breaks down and frees the mineral content of bones to compensate for low calcium levels. This process is also known as bone resorption [8].

Vitamin D

PTH also increases the amount of vitamin D that is converted to its active form, calcitriol. Active vitamin D increases calcium absorption in the gut and limits the amount of calcium being excreted [8].

Phosphorus

Phosphorus binds to calcium. When phosphorous rises in the blood, calcium levels drop. Conversely, if phosphorus becomes depleted, calcium levels rise. This can sometimes lead to hypercalcemia (high calcium) [5].

Magnesium

Last, but not least, calcium levels are dependent on magnesium. When magnesium levels are normal, calcium is not affected. But if magnesium levels are low, it can suppress the amount of PTH being secreted. This leads to a drop in calcium levels. Magnesium deficiency can be a cause of hypocalcemia (calcium deficiency) [5].

Hyperparathyroidism: An Underdiagnosed Condition

Hyperparathyroidism or an overactive parathyroid gland is the most common cause of hypercalcemia (high calcium). An enlargement of one or more of your parathyroid glands (either benignly or due to cancer) will cause this condition [9, 10].

Primary doctors often fail to recognize hyperparathyroidism, even when calcium levels are too high (over 10.5 mg/dL). According to one study, above-range calcium levels were missed or ignored in 58% of cases. Even when both calcium and PTH were above range, a diagnosis was missed in 28% of cases. Women were more likely than men to have their symptoms ignored [11].

Another study found that doctors missed diagnosis of hyperparathyroidism in 40% of cases, even when both calcium and PTH were well above the normal range. High blood calcium was often wrongly ascribed to other causes, such as diuretics, calcium supplements, dehydration, and kidney dysfunction [12].  

The problem gets even more challenging in people with “normal” calcium levels and hyperparathyroidism. This condition is particularly underdiagnosed in the elderly. Older people who have levels of 10.8 mg/dL are often sent off as “normal.” Doctors will tell them that “everything looks good.”

As a result, their parathyroid disorder might go untreated (or wrongly treated!) for years, leading to numerous health complications.

Symptoms

Common symptoms of hyperparathyroidism include [13, 14, 15, 16]:

  • Kidney stones
  • Muscle weakness
  • Slow digestion
  • High blood pressure and other heart problems
  • Fragile bones/frequent bone fractures (especially in postmenopausal women)
  • Impaired cognition
  • Depression
  • Anxiety

If you’re above 60 years old, experiencing symptoms of hyperparathyroidism, and your healthcare provider is telling you your calcium labs look fine, you may need to take their words with a grain of salt. You might need to see an endocrinologist to discuss your health status and lab results [11].

Seasonal Variation

In a study of 90 young, healthy people in South Italy, vitamin D levels were higher and PTH levels lower over the sunny summer months [17].

Lack of sun seemed to negatively affect only the women, of which 30% were deficient in vitamin D and calcium over the winter months. The deficiency was mild and of the type that often goes unnoticed. On the other hand, men maintained higher vitamin D, PTH, and calcium levels throughout the year [17].

Given that Italy’s winters are not harsh, more drastic changes could be expected in people living further up the Northern hemisphere. Whether such changes in calcium levels over the winter are significant enough and “normal” remains to be determined.  

Optimal Levels

As you were able to see, the “normal” range of blood calcium levels is relatively wide and un-robust. If your levels are slightly outside this range, doctors will rarely pay attention to them. Experts can barely agree on the values that define the normal, let alone on what should be considered optimal.

A handful of studies suggest that people should aim for a much narrower optimal range to lower their health risks.

In a study of more than 18k patients admitted to various hospitals, the fewest number of deaths occurred in those with blood calcium levels between 9.6 – 10.1 mg/dL. Patients with higher or lower calcium levels were more likely to die [18].

Another study examined the link between calcium and the risk of heart attacks in a population of one million adults. According to their findings, people with blood calcium levels under 9.55 mg/dL are at two-fold increased risk of heart attacks [19].

Other studies suggest that levels over 9.8 mg/dL increase the risk of death and heart disease, while the lowest risk of dying was found for those with blood levels between 9.4 – 9.5 mg/dL [20].

If you think your blood calcium levels are suboptimal, you may want to look into safe ways of increasing or decreasing your values. Be sure to consult a healthcare professional to address any underlying causes of your condition.

Irregular Calcium Levels?

LabTestAnalyzer helps you make sense of your lab results. It informs you which labs are not in the optimal range and gives you guidance about how to get them to optimal. It also allows you to track your labs over time. No need to do thousands of hours of research on what to make of your lab tests.

LabTestAnalyzer is a sister company of SelfHacked. The proceeds from your purchase of this product are reinvested into our research and development, in order to serve you better. Thanks for your support.

Takeaway

Despite the common consensus, the latest research suggests there is no one-size-fits-all normal range for calcium levels. What is “normal” can be influenced by age, gender, health status, and even seasonal variation.

A big challenge older people face is having a hyperparathyroid disorder go undiagnosed for years, despite usually having borderline-high calcium levels. Qualified endocrinologists will know how to recognize and treat this disorder.

About the Author

Jimmy Julajak, MSc

MS (Psychology)

Jimmy got his MSc from the University of Copenhagen.

Jimmy is a psychologist and researcher. He is particularly interested in the workings of the brain and strategies for improving brain health. He believes that people shouldn't hand over the responsibility for their health only to their doctors. His aim is to empower each person with easy-to-understand, science-based health knowledge.

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