Alkaline phosphatase requires zinc and magnesium as cofactors so assessment of both nutrients would be prudent when alk phos is suboptimal.
Alkaline phosphatase requires magnesium as well as zinc so it would be prudent to check serum or RBC magnesium with a low Alk Phos and optimal Zinc levels. Also assess for low magnesium intake, malabsorption, and chronic alcohol ingestion.
One cross-sectional study of 42 individuals with alkaline phosphatase below 45 U/L and 45 controls looked at zinc and magnesium levels. Deficiency of zinc was found in 47.62% of those with low alk phos activity, while 52.38% were found to be magnesium deficient. Both zinc and magnesium were significantly lower in subjects versus controls (Ray 2017).
Causes of low alkaline phosphatase besides zinc and magnesium deficiency include Wilson’s disease (copper displaces zinc), hypothyroidism, pernicious anemia, and congenital hypophosphatemia (Lowe 2021).
References
Lowe, Dhruv, et al. “Alkaline Phosphatase.” StatPearls, StatPearls Publishing, 11 August 2021.
Ray, Chinmaya Sundar, et al. "Low alkaline phosphatase (ALP) in adult population an indicator of zinc (Zn) and magnesium (Mg) deficiency." Current Research in Nutrition and Food Science Journal 5.3 (2017): 347-352.