What is Alkaline Phosphatase?
Alkaline phosphatase (ALP) is a glycoprotein-structured metalophosphatase that is present in many tissues of all living beings, from bacteria to mammals [1]. It is a membrane-bound enzyme that catalyzes the hydrolysis of phosphate monoesters at basic pH values [2]. This enzyme is divided into four isozymes depending on the site of tissue expression: Intestinal ALP, Placental ALP, Germ cell ALP, and tissue nonspecific alkaline phosphatase or liver/bone/kidney (L/B/K) ALP [2].
What Does Alkaline Phosphatase do?
ALP is produced by nearly every cell and tissue and plays multiple roles in the body involved in different metabolisms, signal transduction and cellular regulation [3]. It has been suggested that the bone isoenzyme is involved in mammalian bone calcification and the intestinal isoenzyme in the active transport of phosphate into the epithelial cells of the intestine [2].
In the setting of sweat glands, it appears that ALP is related to membrane transport, with a role in the production of primary sweat secretions at intercellular canaliculi [4].
Additionally, ALP is widely used for enzyme-linked immunosorbent assays. It is also an important clinical diagnostic biomarker because its abnormal activity in the body is closely related to many diseases [3].
What are the causes of elevated Alkaline Phosphatase levels?
Hyperphosphatasemia
Hyperphosphatasemia (elevated blood activity or concentration of ALP) is most often evidence of liver problems or gallbladder disease, but can also be linked to osteomalacia (softening of bones), or malnutrition. Less commonly, blood ALP levels are positively correlated with kidney tumours, bowel upset, pancreas problems, or a systemic infection [5].
Certain conditions associated with hyperphosphatasemia are sepsis, malignant obstruction and AIDS. One study of hospitalised patients with ALP values over 1,000 U/l found the cause to be sepsis in 10 patients, eight of the patients had biliary obstruction and nine had AIDS [6].
Transient hyperphosphatasemia is a harmless condition characterised by extremely high serum ALP levels seen at the age of 13 to 24 months, which resolves spontaneously after 5 to 20 weeks [7].
Diet and Alkaline Phosphatase
How does diet influence Alkaline Phosphatase levels?
The diet of an organism has a significant influence on the body’s ALP concentrations. One of the crucial dietary components controlling ALP levels is dietary fat. One study discovered that ALP activity in serum and intestinal mucosa multiplied in rats fed with fish oil [8]. Likewise, a separate study on healthy young adult humans observed augmentation of ALP concentrations in the blood after a fatty meal [9].
Dietary nutrients also affected the activity of BAP (bone-specific ALP) as labile activity correlated significantly with serum phosphorus, calcium intake or phosphorus intake [10].
Furthermore, besides fat and other nutrient intake, some beverages and/or chemicals can influence ALP activity, with polyphenols and polyphenol-rich beverages such as tea and wine reported to inhibit the activity of ALP in human vascular smooth muscle cells[11].
What foods should be avoided if Alkaline Phosphatase is high?
High-fat meals can increase ALP activity, particularly in individuals with blood types B or O. One study found ALP levels were 8.8% and 5.2% higher 14 hours after a large portion of a high-fat meal versus a low-fat meal [12]. So limit intake of high-fat foods such as fried foods, fatty meats and full-fat dairy foods.
There are beverages with compounds – including those in tea, wine, beer and polyphenols – that have been reported to inhibit ALP activity [11]. However, ALP levels in humans from these beverages have not been characterised, everything should be consumed in moderation.
Conclusion
In conclusion, diet influences Alkaline Phosphatase levels, especially the fat intake, nutrient composition and the consumption of liquid food and beverages. However, the specific mechanisms are very complicated and could be different based on different chronic diseases and genetic susceptibility. If an individual's Alkaline Phosphatase levels are high, it should be discussed with a doctor as to which specific foods should be avoided to maintain normal and healthy levels.