Alkaline phosphatase is one of the older liver-panel staples and one of the markers clinicians most often dismiss. The longevity literature has spent the last 15 years rehabilitating it as a quiet predictor of cardiovascular and all-cause mortality. The mechanism is not fully understood, but the empirical pattern across cohorts is consistent enough that Levine's PhenoAge model weights it positively.
What is alkaline phosphatase?
Alkaline phosphatase is a family of enzymes that catalyze the hydrolysis of phosphate esters at alkaline pH. Four genes encode tissue-specific isoenzymes: liver/bone/kidney (sharing the ALPL gene with post-translational differences), intestinal, placental, and germ-cell. In healthy non-pregnant adults, total serum ALP is roughly 50% liver-derived and 50% bone-derived, with small intestinal contributions.
The composite nature is why ALP requires careful interpretation. A reading of 130 U/L can reflect liver disease, bone turnover, or a mix of both. Isoenzyme fractionation (gamma-glutamyl transferase, or specifically the bone-specific ALP isoform) sharpens the source.
What is a normal alkaline phosphatase range?
Standard ranges:
- Adult: 40-130 U/L (most US labs).
- Pregnancy, third trimester: up to 250 U/L is normal (placental contribution).
- Children and adolescents: substantially higher, up to 400-500 U/L during growth spurts (active bone turnover).
Adult population means sit around 70-85 U/L. The longevity-optimal band is 40-90 U/L; values above 100 within the reference range carry a measurable mortality gradient.
Tonelli et al. 2009 examined ALP in a post-MI cohort (n=1,485) and found that participants in the highest quintile of ALP (>=110 U/L) had 1.5x all-cause and cardiovascular mortality at 3-year follow-up compared to the lowest quintile, independent of liver enzymes, kidney function, and traditional cardiovascular risk factors Tonelli et al. 2009, n=1485 . Multiple subsequent cohorts have replicated the gradient in healthier populations.
Longevity-optimal framing:
- 40-70 U/L: optimal.
- 70-90 U/L: still good.
- 90-110 U/L: monitor; investigate if drifting.
- 110-130 U/L: soft flag; targeted workup.
- >130 U/L: investigate; isoenzyme fractionation if cause unclear.
How it feeds into PhenoAge
Levine et al. 2018 included serum alkaline phosphatase as one of the nine PhenoAge inputs Levine et al. 2018 . The coefficient is positive: higher ALP raises calculated phenotypic age. The slope is moderate; differences within the normal range have a smaller effect on PhenoAge than CRP or RDW differences. Run the calculator with your CMP to see your specific contribution.
What does high alkaline phosphatase mean?
Three frames for the mortality association:
- Vascular calcification. ALP is co-expressed in vascular smooth muscle cells during arterial calcification; serum ALP correlates with coronary artery calcium scores in some cohorts. The mechanistic link to mineral metabolism (phosphate, FGF-23, klotho) is active research. ALP is not a calcium score, but it points in the same direction.
- Liver fat and metabolic disease. Mild ALP elevation often accompanies non-alcoholic fatty liver disease (NAFLD/MASLD). Kunutsor et al. 2014 meta-analyzed 17 cohorts and found elevated GGT, ALT, and ALP each independently predicted incident type 2 diabetes Kunutsor et al. 2014 . The shared upstream is hepatic fat and metabolic syndrome.
- Bone turnover. Active bone remodeling raises ALP via the bone-specific isoform. This is normal in adolescence and pregnancy; in older adults it may flag osteoporosis with high turnover, healing fractures, vitamin D deficiency, hyperparathyroidism, or Paget's disease.
What drives it
Causes of mildly to moderately elevated ALP in adults, ordered by frequency:
- Hepatic origin.
- Cholestasis (intra- or extrahepatic bile duct obstruction). Pair with elevated GGT to confirm liver source. Suspect when ALP rises with GGT in parallel.
- Non-alcoholic fatty liver disease (NAFLD/MASLD). Often subtle ALP elevation with normal or mildly elevated ALT/AST.
- Drug-induced cholestatic injury: many medications including some antibiotics, anabolic steroids, certain SSRIs.
- Primary biliary cholangitis.
- Bone origin.
- Vitamin D deficiency with secondary hyperparathyroidism. Common; fixable.
- Healing fractures (transiently elevated for 6-12 weeks).
- Osteoporosis with high turnover.
- Paget's disease of bone (markedly elevated, often >300 U/L).
- Hyperparathyroidism (primary or secondary).
- Bone metastasis.
- Other.
- Pregnancy (placental ALP; expected and benign).
- Certain anticonvulsants.
- Heart failure with hepatic congestion.
Causes of low ALP (<40 U/L) are uncommon and include hypothyroidism, magnesium or zinc deficiency, malnutrition, and the rare genetic condition hypophosphatasia.
Modifiable drivers
For mildly elevated ALP without overt disease, the actionable interventions:
- Address NAFLD/MASLD. A 5-10% body weight loss in overweight adults typically reduces ALP, ALT, and GGT in parallel within 3-6 months. Lower refined carbohydrate intake, higher fiber, weight training, and aerobic exercise all contribute. See the GLP-1 article for the pharmacologic option.
- Replete vitamin D. Maintain 25(OH)D >30 ng/mL; if deficient, 2,000-4,000 IU/day cholecalciferol corrects most adults within 8-12 weeks. See the vitamin D and K2 stack article.
- Reduce alcohol. Heavy drinking raises ALP via both hepatic and biliary mechanisms; cessation reverses within 2-3 months.
- Review medications. Anabolic steroids, certain anticonvulsants, and some antibiotics can raise ALP; review with prescriber if unexplained elevation.
- Maintain adequate dietary protein and calcium. Underrated for bone turnover; very-low-protein diets are bone-stressful.
There is no supplement that directly lowers ALP in healthy adults without an underlying deficiency or disease. The work is on the upstream cause.
What about isolated low ALP?
Persistent ALP <40 U/L is uncommon but worth noting. Consider hypothyroidism, hypophosphatasia (rare genetic disease, can cause dental and skeletal issues), severe magnesium or zinc deficiency, and protein-calorie malnutrition. In well-fed adults with normal thyroid function, low ALP is rarely actionable but flags a workup if persistent.
Cross-marker patterns
Read ALP alongside GGT, ALT, AST, and bilirubin for the liver picture. ALP elevation with GGT elevation = hepatic source. ALP elevation with normal GGT but elevated calcium and parathyroid hormone = bone or parathyroid source. ALP plus 25(OH)D and PTH gives the bone metabolism context.
For PhenoAge specifically, ALP pairs with albumin, creatinine, and glucose as the "organ-function" subset of the formula.
How to act on yours
Testing cadence:
- Healthy adult: annual CMP with ALP.
- ALP 90-110 U/L: redraw in 6 months; investigate if trending upward.
- ALP 110-130 U/L: targeted workup. GGT, ALT, AST, 25(OH)D, PTH, calcium. Consider abdominal ultrasound if liver markers also elevated.
- ALP >130 U/L: clinical workup. Add isoenzyme fractionation if source unclear.
If your ALP drifts from 75 to 105 U/L over 18 months in the absence of new medications: pull GGT, the liver enzymes, vitamin D and PTH. Most cases will turn out to be early NAFLD or mild vitamin D deficiency, both of which are addressable.
Counter-view
Some clinicians treat any ALP within the reference range as benign and dismiss the within-range mortality gradient as residual confounding. The cohort data is reasonably consistent across diverse populations, but the absolute risk increase is small. The pragmatic position: ALP is a soft marker on its own. Drift is more meaningful than absolute level. If your ALP is 95 and your liver, bone, and metabolic markers are clean, that is not actionable; if it has moved from 70 to 95 over 2 years, that is.
