Vitamin D is a fat-soluble vitamin that works more like a hormone than a typical vitamin. Your skin makes it when exposed to UVB sunlight, and smaller amounts come from oily fish, egg yolks and fortified foods. Whether from the sun or supplements, it is inactive at first. The liver converts it to 25-hydroxyvitamin D, the form measured in blood tests, and the kidneys then convert it to calcitriol, the active hormone. Calcitriol binds to vitamin D receptors found in many tissues. In the gut, it increases the absorption of calcium and phosphate, which is essential for bone and muscle function. Vitamin D3 (cholecalciferol) is the animal-sourced form and is generally more effective at raising blood levels than D2 (ergocalciferol), which is plant or fungal. Being fat-soluble, it is better absorbed with a meal containing fat. Australians can be low in winter or if they cover up or have limited sun exposure (NIH Office of Dietary Supplements).

• Helps maintain healthy bones and teeth
• Helps support normal calcium absorption
• Helps maintain normal muscle function
• May help support normal immune system function
• Helps relieve vitamin D deficiency when dietary intake and sun exposure are inadequate
• May help support mood and wellbeing during the winter months

What is the best time of day to take vitamin D?

Whenever you will remember, with a meal that contains some fat. Fat helps your body absorb it. There is no strong evidence that morning or evening makes a difference.

Do I need vitamin D if I live in Australia?

Many Australians make enough from sunlight in summer, but levels can drop in winter, in southern states, or if you work indoors or cover up. A blood test from your doctor is the best way to know your level.

Vitamin D is fat-soluble and can build up, so do not exceed the label dose without advice, as too much can raise blood calcium. Speak to a healthcare professional if you take medicines such as thiazide diuretics or have kidney or parathyroid conditions.