Vitamin D3 4000iu (60 Tabs) Natures Aid Vitamin D3 contributes to: The maintenance of normal bones, teeth, muscle function. Benefits: Prevention of deficiency including vegans, dark-skinned people, alcoholics, people with kidney, liver or coeliac disease. Seasonal Affective Disorder. Supplementing with vitamin D can often produce improvements in mood in those with SAD in as little as aweek. Bone Health as Vitamin D plays a key role in the regulation of calcium and phosphorus levels in the blood by promoting absorption in the intestines and calcium re-absorption in the kidneys. This leads to normal calcification ofthe bone matrix, needed for bone growth and repair. Immune Health as Vitamin D plays a role in the immune system by virtue of the fact that it promotes the process ofphagocytosis (where immune cells engulf bacteria etc.), anti-tumour activity and a modulating effect onthe immune system.