Vitamin D plays a key role in promoting calcium absorption in the intestine and maintaining adequate blood calcium and phosphate concentrations to enable normal bone mineralization. In this way, vitamin D is important for the proper functioning of the skeleton, and may prevent that bones to become brittle as in osteoporosis.

Other effects

Vitamin D has beneficial effects on muscle function and strength. The vitamin is also involved in cell growth, neuromuscular and immune function and reduction of inflammation. There is accumulating epidemiologic data that a low vitamin D status is inversely associated with disorders such as diabetes, rheumatoid arthritis and multiple sclerosis.
The European Food Safety Authority (EFSA) has acknowledged the following beneficial effects as a basis for health claims:
• Vitamin D contributes to the maintenance of normal muscle function
• Vitamin D contributes to the normal function of the immune system and healthy inflammatory response
• Vitamin D contributes to the normal absorption/utilisation of calcium and phosphorus and maintenance of normal blood calcium concentrations
• Vitamin D contributes to the normal cell division
• Vitamin D contributes to the maintenance of normal bones
• Vitamin D contributes to the maintenance of normal teeth

Vitamin K includes two natural vitamers: vitamin K1 and vitamin K2:

Vitamin K1

Vitamin K1, also known as phylloquinone, is made by plants, and is found in highest amounts in green leafy vegetables. It performs the classic functions of vitamin K, including its activity in the production of blood coagulation proteins.
Bacteria in the gut flora can convert K1 into vitamin K2.

Vitamin K2

Vitamin K2 or menaquinone, has a similar mechanism of action as vitamin K1. It is suggested that it plays a key role in bone strength and arterial health.
EFSA has acknowledged the following beneficial effects as a basis for health claim:
• Vitamin K contributes to normal blood clotting
• Vitamin K contributes to the maintenance of normal bones