Table 1 Summary of possible factors affecting calcium absorption across the intestinal epithelium

Extrinsic/luminal

 Ca²⁺ (long-term low luminal Ca²⁺ or    low calcium diet)

Increase expression of TRPV5/6, CaBP-D_9k, NCX1, PMCA_1b,

Increase activity of PMCA_1b and NCX1

N/A

↑

[4, 8, 10]

  Ca²⁺ (prolong exposure to high luminal   Ca²⁺)

Possibly by increase FGF-23 expression (Ca²⁺ > 30 mM) and inhibit transcellular transport by unknown mechanism

N/A

↓

[84]

  Iron

N/A

N/A

↓

[58]

  Glucose/galactose (SGLT1 substrates)

Decrease Ca_v1.3 activity

Increase solvent drag-induced paracellular calcium flow

↑

[52, 91]

  Amino acids

N/A

Increase NHE activity

↑

[96]

Increase nutrient-induced paracellular calcium flow

  Fructose

Decrease expression of TRPV6 and CaBP-D_9k

N/A

↓

[27, 28]

Intrinsic

  Hormone

    1,25(OH)₂D₃

Increase expression of TRPV5/6, CaBP-D_9k, NCX1, PMCA_1b

Stimulate nongenomic signaling pathways involving PI3K, PKC, and MEK to enhance calcium transport

↑

[32, 40]

Increase expression of claudin-2, 12

    PTH

Increase calcium uptake

(Unknown mechanism)

N/A

↑

[71]

    FGF-23

Decrease 1,25(OH)₂D₃-enhanced expressions of TRPV5/6, CaBP-D_9k

Decrease 1,25(OH)₂D₃-enhanced paracellular calcium transport and calcium permeability

↓

[53, 54]

 Paracrine

    FGF-23

Increase CaSR activity

N/A

↓

[84]

    Stanniocalcin-1

Decrease expression of TRPV5/6, CaBP-D_9k

N/A

↓

[107]

No change in the expression of NCX1, PMCA_1b

Neural (ENS)

    VIP

N/A

N/A

↑

(Indirect evidence)

[73]