Vitamin k, D-chiro Inositol and α-lactalbumin in Bone Homeostasis

Recommendations regarding the ideal daily intake of calcium and vitamin D vary based on the anthropometric characteristics and comorbidities of patients. An adequate level of these two nutrients is recommended especially in patients undergoing treatment with anti-resorptive drugs used for both preventive and therapeutic purposes in osteoporosis. This occurs in women with breast cancer, in whom the marked tissue hypoestrogenism induced by adjuvant therapy (aromatase inhibitors and/or tamoxifen ± GnRH analogues) causes a significant acceleration in bone loss (CTIBL-Cancer Treatment-Induced Bone Loss), with a consequent increased risk of fracture from the first year of therapy. It is therefore essential to start treatment with antiresorptive drugs and calcium and vitamin D supplementation in order to safeguard bone health and prevent secondary osteoporosis.

Optimal serum concentrations of calcium and vitamin D play a central role in bone health, but insufficient intake can depend on numerous factors, including diet and the presence of other nutrients, as well as the body's ability to absorb them effectively. It has been hypothesized that vitamin K and α-lactalbumin improve the absorption of calcium and vitamin D. Vitamin K is a fat-soluble vitamin that comes in various forms, including vitamin K2 (menaquinone), which is involved in bone remodeling. It promotes gamma-carboxylation of osteocalcin, causing its activation and leading to increased incorporation of hydroxyapatite into bone, resulting in increased uptake of calcium from the blood and other tissues. High levels of the uncarboxylated form of osteocalcin, which is found in cases of vitamin K deficiency, have been associated with an increased risk of fractures despite adequate therapy with oral bisphosphonates. Studies have reported that a combination of alendronate and vitamin K2 can lead to a decrease in the ratio of uncarboxylated osteocalcin to carboxylated osteocalcin, contributing to an increase in BMD, especially in the femoral neck, thus reducing the risk of fragility fractures. α-Lactalbumin is a small acidic protein that has a binding site with high affinity for Ca++. The bioaccessibility of Ca++, i.e., the amount of micronutrient potentially available for absorption in the human body, depends on the amount of soluble calcium released from food processing during digestion. It has been hypothesized that binding to peptides such as α-lactalbumin may increase bioaccessibility due to its ability to prevent precipitation at the neutral pH present in the absorptive tracts of the small intestine. In addition, α-lactalbumin has a binding site for vitamin D3, and complexes consisting of monomers of this protein and vitamin D have shown good stability in the presence of high vitamin concentrations. It is also known from in vitro studies that α-lactalbumin can improve the intestinal absorption of D-chiro-inositol by as much as 10 times compared to the absence of this protein in the intestine.

The combination of vitamin K, α-lactalbumin, and D-chiro-inositol should improve the intestinal absorption of calcium and vitamin D, increasing the percentage of patients able to achieve normalization of serum vitamin D levels and urinary calcium excretion (understood as a parameter of adequate calcium intake). This aspect, together with the direct effect of these components on bone remodeling, could enhance the antiresorptive effect of standard bisphosphonate therapy, improving the quantitative and qualitative parameters of bone.

Inositol is a carbohydrate structurally similar to glucose which, in its D-chiro-inositol isomeric form, acts on bone remodeling by blocking the activation of osteoclasts through inhibition of the binding of RANK-L to its receptor present on pre-osteoclasts.

Therefore, we design a prospective randomized pilot study aims to evaluate the effect of synergistic effect of vitamin K, α-lactalbumin and D-chiro-inositol supplementation compared to standard therapy with calcium carbonate and vitamin D alone on calcium-phosphorus metabolism parameters and bone mineral density in patients with breast cancer treated with alendronate for the prevention of bone damage from hormone therapy.

Inclusion criteria

• caucasian women aged between 35 and 70;
• diagnosed with breast cancer undergoing treatment with aromatase inhibitors or tamoxifen + GnRH analogues or aromatase inhibitors + GnRH analogues not started more than 12 months ago, about to start treatment with oral bone resorption inhibitors (alendronate);
• vitamin D levels below 30 ng/ml (test carried out no more than 6 months prior to the baseline/T0 visit)
• patients able to comply with the procedures and/or requirements of the study
• informed consent to participate in the study and data processing, written personally and/or through a witness, before any study-specific procedure is carried out

Exclusion criteria

• uncontrolled diabetes mellitus (HbA1c 8%), severe CRF (eGFR<30 ml/min);
• patients with primary or secondary hyperparathyroidism due to CRF;
• baseline vitamin D levels greater than 30 ng/ml;
• patients already being treated with anti-resorptive drugs;
• patients undergoing steroid therapy;
• patients undergoing treatment with other forms of vitamin D (calcifediol, calcitriol) or who require high doses of calcium (hypoparathyroidism);
• patients undergoing treatment with drugs that can affect calcium excretion (diuretics);
• inability to comply with the procedures required by the study.