What it measures.
Alkaline Phosphatase (ALP) is an enzyme found in liver, bone, kidneys, and intestines. Traditionally used to diagnose liver and bone disorders, ALP is increasingly recognized as a biomarker of biological aging. Both very high and very low levels are associated with increased mortality. In the context of longevity, optimal ALP suggests healthy bone turnover and liver function.
The blood activity level of alkaline phosphatase enzyme, measured in U/L. Since ALP comes from multiple sources (liver, bone, intestine), elevated levels require additional tests to determine the origin.
Why it matters.
Elevated ALP indicates liver disease (especially biliary obstruction) or bone disorders (Paget's disease, bone metastases). But moderately elevated ALP also predicts cardiovascular disease and mortality independent of liver disease. Low ALP can indicate malnutrition or rare genetic conditions. For biological age assessment, ALP provides insight into systemic health.
Physiology.
ALP is a group of isoenzymes that hydrolyze phosphate esters in alkaline pH. Bone ALP is released during bone formation (osteoblast activity). Liver ALP is induced by bile duct obstruction. Intestinal ALP relates to fat absorption. In pregnancy, placental ALP is released. Total ALP is the sum of all sources.
Testing & preparation.
How to prepare
- Fasting preferred (eating raises intestinal ALP)
- Note medications that affect liver or bone
- If elevated, may need GGT and isoenzymes to determine source
When to test
Part of standard metabolic panels; specifically for liver or bone disorders, or biological age assessment
How often
Annually for general health; more often if liver/bone conditions
Interpretation.
High alkaline phosphatase
Common causes:
- Bile duct obstruction (stones, strictures, cancer)
- Liver disease (hepatitis, cirrhosis, medications)
- Bone disorders (Paget's disease, bone metastases, fracture healing)
- Pregnancy (placental ALP)
- Healing fractures
- Adolescent growth spurts (normal in children)
- Chronic kidney disease
- Vitamin D deficiency (causes secondary bone turnover)
Implications:
- If isolated elevation: check GGT (elevated = liver source; normal = bone source)
- Biliary elevation: investigate obstruction (imaging)
- Bone elevation: evaluate for metastases or metabolic bone disease
- Even modest elevation associated with cardiovascular mortality
Low alkaline phosphatase
Common causes:
- Malnutrition
- Zinc deficiency (ALP is a zinc-dependent enzyme)
- Hypophosphatasia (rare genetic disorder)
- Celiac disease
- Severe anemia
- Hypothyroidism
- Post-cardiac bypass surgery
Implications:
- Very low (<30 U/L): consider hypophosphatasia or malnutrition
- May affect bone mineralization
- Associated with increased fracture risk if hypophosphatasia
Optimization.
Diet
- Adequate zinc (ALP is zinc-dependent)
- Vitamin D to prevent secondary bone turnover
- Moderate fat intake (high fat increases intestinal ALP)
- Limit alcohol (liver protection)
Lifestyle
- Weight-bearing exercise for healthy bone turnover
- Limit alcohol to protect liver
- Avoid hepatotoxic supplements
Supplements
- Zinc if deficient (supports normal ALP function)
- Vitamin D to prevent compensatory elevation
- Vitamin K2 for bone health
FAQs.
My ALP is elevated but my liver feels fine—what's going on?
ALP comes from multiple sources. Elevated ALP with normal GGT (gamma-glutamyl transferase) suggests bone origin rather than liver. Causes include vitamin D deficiency, bone metastases, Paget's disease, or normal healing after fracture. If GGT is also elevated, liver/biliary source is likely and needs imaging.
Why is ALP included in biological age panels?
Large population studies show that ALP independently predicts all-cause and cardiovascular mortality, even within 'normal' range. Higher ALP reflects systemic dysfunction—vascular calcification, inflammation, or subclinical liver/bone disease. For biological age assessment, optimal ALP in the lower-normal range suggests healthier aging.
My teenager has very high ALP—should I be worried?
Probably not. Children and adolescents normally have ALP 2-3 times adult levels due to active bone growth. This is entirely physiological and decreases after growth plates close. Only investigate if levels are extremely high or if there are symptoms of bone disease.