Low Alkaline Phosphatase (ALP): What It Means and What Causes It

Low alkaline phosphatase (ALP, alk phos) can point to a nutritional shortfall, low thyroid function, a medication, or a recent acute illness. A persistently low result with bone or dental symptoms can also point to the rare genetic condition hypophosphatasia.

Published

April 23, 2026

Last updated

September 24, 2026

Read time

10 min read

Medically reviewed by

Rhonda Collins, FNP-C

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Low alkaline phosphatase (ALP, below 44 IU/L in adults) means your body is making less of this enzyme than expected. The common causes are a shortfall in zinc or magnesium, low thyroid function, malnutrition, a medication, or a recent acute illness or surgery. ALP is also written “alk phos” on many lab reports. A single low alk phos result is often temporary and not significant on its own, and a repeat test is the usual first step. A value that stays low on repeat testing, especially with bone or dental problems, can point to hypophosphatasia, a rare inherited condition. See the Alkaline Phosphatase biomarker overview for how ALP is measured.

What a Low Alkaline Phosphatase Result Means

ALP is a zinc-dependent enzyme. Its activity requires adequate zinc and magnesium as cofactors, so when these are depleted, ALP activity falls. Thyroid hormone also upregulates ALP production, so hypothyroidism reduces it. The most clinically significant cause of persistently low ALP is hypophosphatasia, a rare genetic disease caused by mutations in the ALPL gene that encodes ALP itself. It results in impaired bone mineralization and accumulation of ALP substrates in tissues.

What Causes Low Alkaline Phosphatase

Most causes of low alkaline phosphatase are nutritional, hormonal, or temporary, and a few are genetic. MedlinePlus, Cleveland Clinic, and a review of low ALP in adults by Riancho (2023) list these:

• Zinc deficiency. ALP requires zinc as a structural cofactor, so depletion reduces enzyme activity.
• Magnesium deficiency, which plays a supporting role in ALP activity.
• Hypothyroidism. Thyroid hormone upregulates ALP, so low thyroid output depresses it.
• Malnutrition and protein deficiency.
• Vitamin B12 deficiency, including pernicious anemia.
• Wilson disease, a rare inherited disorder of copper metabolism.
• Severe acute illness or injury, where a low ALP is a temporary side effect of the illness.
• Cardiac surgery with cardiopulmonary bypass. In one study, ALP fell sharply the day after bypass surgery and recovered toward normal over about ten days. The drop was not explained by blood dilution alone.
• Hypophosphatasia, a rare inherited condition caused by variants in the ALPL gene. It ranges from severe forms in infants to mild forms first noticed in adulthood.

In a review of 83 veterans with a low ALP result, Lum (1995) found that cardiac surgery with bypass, malnutrition, magnesium deficiency, hypothyroidism, and severe anemia were the associated conditions seen. About half had none of the conditions previously linked to low ALP, and none had clinically apparent hypophosphatasia.

Medications That Can Cause Low Alkaline Phosphatase

Several medications are linked to low alkaline phosphatase results. Hospital studies of adults with low ALP treat the first four groups below as secondary causes to rule out before considering hypophosphatasia:

• Bisphosphonates and other antiresorptive osteoporosis drugs, which slow bone turnover.
• Glucocorticoids (corticosteroids such as prednisone).
• Fibrates, including clofibrate.
• Chemotherapy and immunosuppressant drugs.
• Birth control pills. MedlinePlus notes they may lower ALP levels.
• Estrogen hormone therapy after menopause. In a one-year trial in early menopausal women, estrogen with progestin lowered bone turnover markers, including ALP.

A medication effect is one reason a clinician asks for a full medication list before interpreting a low alk phos result.

Autoimmune and Malabsorption Causes of Low Alkaline Phosphatase

Three autoimmune conditions can lower alkaline phosphatase, through either nutrient absorption or thyroid function:

• Celiac disease. Celiac disease is an immune disorder that damages the small intestine and can keep the body from absorbing the nutrients it needs. It appears on published lists of acquired causes of low ALP, likely through that malabsorption.
• Pernicious anemia. Pernicious anemia is an autoimmune condition in which the body attacks intrinsic factor, the protein needed to absorb vitamin B12. MedlinePlus lists it as a possible cause of low ALP.
• Hashimoto’s disease. Hashimoto’s disease is an autoimmune disorder and the most common cause of hypothyroidism, according to the NIH. Low ALP from Hashimoto’s works through the low thyroid function it causes.

Other malabsorption conditions can lower ALP in the same way when they reduce zinc, magnesium, or protein status.

One Low Result vs. a Persistently Low Result

A single low alkaline phosphatase result can follow an acute illness or surgery and often returns to normal on its own. Riancho (2023) describes low ALP as a byproduct of many severe acute injuries and diseases. In the bypass study above, ALP recovered toward normal within about ten days.

A persistently low result means ALP stays low on repeat tests taken weeks apart. Researchers who study low ALP in adults define it this way because it separates temporary drops from an ongoing cause. Even then, most persistent cases have an explanation other than hypophosphatasia. In a review of two Brazilian hospitals, Vieira and colleagues (2021) found 410 adults with ALP confirmed low on at least two tests. They excluded 398 of them because a secondary cause, such as a medication or another illness, explained the result.

Reading Low ALP Alongside Zinc, Magnesium, Phosphate, and Vitamin B12

Low alkaline phosphatase is easier to interpret when it is read with a few related markers, because each one points toward a different cause.

• Zinc and magnesium. A low zinc or low magnesium result alongside low ALP fits a cofactor shortfall, since ALP needs both minerals to work.
• Vitamin B12. A low vitamin B12 result alongside low ALP fits B12 deficiency or pernicious anemia.
• Thyroid markers. A high TSH alongside low ALP fits hypothyroidism.
• Phosphate and vitamin B6. These two help separate hypophosphatasia from a nutritional pattern. In a study of 42 adults with unexplained low ALP, Riancho-Zarrabeitia and colleagues (2016) found that those carrying an ALPL gene variant had higher levels of pyridoxal 5’-phosphate (PLP, the main circulating form of vitamin B6) and slightly higher serum phosphate than those without one. Every person in that study with a PLP above the reference range carried a variant.

When low ALP comes with low zinc, magnesium, or B12, the picture points toward nutrition or absorption. When ALP stays low while those markers are normal and PLP is high, the picture points toward hypophosphatasia, as long as the person is not taking vitamin B6. Vitamin B6 supplements, including multivitamins that contain B6, also raise PLP.

When a Persistently Low ALP Warrants a Hypophosphatasia Evaluation

Hypophosphatasia is uncommon, and most low alkaline phosphatase results are explained by something else. An evaluation for it becomes reasonable when ALP stays low on repeat testing, the common causes above have been ruled out, and there are features that fit the condition. In adults those features include early loss of baby teeth, stress fractures or slow-healing fractures, bone or muscle pain, and calcium deposits in joints or tendons.

A hypophosphatasia evaluation usually involves these steps:

• Confirming that ALP is low on repeat tests.
• Reviewing medications and checking zinc, magnesium, vitamin B12, and thyroid function.
• Measuring ALP substrates, which build up when the enzyme is not working. Plasma PLP is a common one. Whyte (2016) describes a high PLP as a sensitive and specific marker for hypophosphatasia. Vitamin B6 supplements and multivitamins also raise PLP, so B6 intake is accounted for before a high PLP is read as a sign of hypophosphatasia. Urine phosphoethanolamine is also used, though less reliably.
• Genetic testing of the ALPL gene. Finding a disease-causing variant confirms the diagnosis, but Riancho (2023) notes that a substantial share of patients have normal results on sequencing.

Many adults found this way have mild disease. In the 2016 Spanish study of 42 adults with unexplained low ALP, about half carried an ALPL variant, and none had major health problems. The diagnosis still matters, because researchers advise caution with bisphosphonates in adults with persistently low ALP.

Symptoms of Low Alkaline Phosphatase

In most cases, low ALP itself produces no direct symptoms. Any symptoms usually come from the underlying cause:

Hypothyroidism signs (if that is the cause):

• Fatigue and cold intolerance
• Weight gain and constipation
• Slow heart rate and dry skin
• Brain fog and depression

Zinc deficiency signs (if that is the cause):

• Poor wound healing
• Taste and smell disturbances
• Skin rashes and hair thinning
• Recurrent infections

Hypophosphatasia (if confirmed):

• Premature loss of deciduous teeth (before age 5) without trauma, a hallmark finding
• Stress fractures and poor bone quality in adults
• Musculoskeletal pain and joint inflammation
• Chondrocalcinosis (calcium deposits in cartilage)
• Nephrocalcinosis in severe childhood forms

Normal ALP Levels

When to See Your Care Team

Book a 1:1 consultation with your care team if ALP is persistently below 44 IU/L, especially with early tooth loss as a child, stress fractures, or joint pain. These patterns raise the possibility of hypophosphatasia. A TSH and zinc level are usually checked first to rule out the more common causes.

Frequently Asked Questions

Is low alkaline phosphatase dangerous?

Low ALP itself is rarely an emergency, but it is a signal to look for the underlying cause. Most low results trace back to a nutritional, thyroid, medication, or temporary cause. Hypophosphatasia is rare but important to diagnose, because it has specific management options, including the enzyme replacement therapy asfotase alfa for severe forms.

How do you raise low alkaline phosphatase?

It depends on the cause. ALP generally moves back toward normal when the cause, such as a mineral shortfall, a thyroid problem, or a medication effect, is identified and addressed. See how to improve your ALP naturally for the nutrition and lifestyle side.

Can a vegetarian or vegan diet cause low ALP?

A plant-based diet is not a cause of low ALP in itself. Low ALP becomes relevant only if the diet leads to zinc deficiency, which can happen with low zinc intake and high phytate intake from legumes and whole grains. A zinc level shows whether that is happening.

Does low ALP mean the liver is underperforming?

Not necessarily. Low ALP is not a marker of liver failure. The liver enzymes relevant to impaired liver function are ALT, AST, and bilirubin. Low ALP reflects reduced ALP production, which is driven by nutritional cofactor status and thyroid function more than liver capacity.

References

• MedlinePlus: Alkaline phosphatase test
• NIH: Hypophosphatasia
• Cleveland Clinic: ALP test
• Riancho JA. Diagnostic approach to patients with low serum alkaline phosphatase. Calcif Tissue Int. 2023
• Riancho-Zarrabeitia L, et al. Clinical, biochemical and genetic spectrum of low alkaline phosphatase levels in adults. Eur J Intern Med. 2016
• Vieira LHR, et al. Active search of adult patients with persistently low serum alkaline phosphatase levels for the diagnosis of hypophosphatasia. Arch Endocrinol Metab. 2021
• Santurtún M, et al. Pain and health-related quality of life in patients with hypophosphatasemia with and without ALPL gene mutations. Front Endocrinol. 2022
• Lum G. Significance of low serum alkaline phosphatase activity in a predominantly adult male population. Clin Chem. 1995
• Lum G, et al. Hypomagnesemia and low alkaline phosphatase activity in patients’ serum after cardiac surgery. Clin Chem. 1989
• Whyte MP. Hypophosphatasia: aetiology, nosology, pathogenesis, diagnosis and treatment. Nat Rev Endocrinol. 2016
• Zhang X, et al. A one-step NIST traceable HPLC method for quantitation of vitamin B6 and 4-pyridoxic acid in human plasma. Pract Lab Med. 2020
• McKiernan FE, et al. Mutational and biochemical findings in adults with persistent hypophosphatasemia. Osteoporos Int. 2017
• Zhu SY, et al. Bone protection for early menopausal women in China: standard or half-dose estrogen with progestin? Gynecol Endocrinol. 2019
• MedlinePlus: Pernicious anemia
• NIDDK: Celiac disease
• NIDDK: Hypothyroidism

Related Resources

• Alkaline Phosphatase: Biomarker Overview
• High ALP Symptoms: Causes, Signs & What to Do
• How to Improve Your ALP Naturally
• ALP vs GGT: Key Differences Explained