Dr Amir Khan issues important advice to anyone taking a vitamin D supplement this winter

Dr Amir Khan appeared on ITV's Lorraine with helpful advice for getting the most out of vitamin D supplements this winter.

Most of the time, sunlight and foods rich in vitamin D are enough to keep up essential nutrient levels. However, as the nights get longer and the weather gets darker, the NHS recommends everyone take a vitamin D supplement.

Speaking to host Lorraine Kelly, Dr Khan said: "Vitamin D is really important in the winter time because we get most of it from sunlight. Our skin makes it but because there isn't enough sunlight we need to supplement it."

A recommended supplement contains 400 international units (IU) a day (1mg of vitamin D equals 40 IU).

"If you haven't already started taking your vitamin D supplement, now is the time to do it," he said. But there's no need to "bother with expensive brands, just get whatever the cheapest brand is".

Vitamin D is "really important for immune health," the doctor says. "It activates new cells, it helps with protective barriers in the skin, the gut, the lungs, and studies show that people with adequate vitamin D levels have less coughs and colds."

However, to allow vitamin D to properly absorb into the body, it has to combine with other nutrients - and magnesium is the most important.

Dr Khan said: "You do need magnesium, what that does is activate the vitamin D. It turns it from its inactive form to an active form so it can do all of its jobs."

You don't have to add a magnesium supplement to the list to do this though, he says. Simply eating more magnesium-rich foods will be enough for most people.

Magnesium-rich foods

• Dark green, leafy vegetables like spinach and kale
• Nuts
• Seeds
• Wholegrains

He also notes that having enough vitamin K2 is important. "One of the jobs of vitamin D is to absorb calcium and take it to the bones and teeth and make them nice and strong. What you don't want is calcium building up in arteries and organs. Vitamin K2 directs it away from them into your bones and teeth," he explains.

"But again, get it from foods rather than supplements, so things like eggs, cheese, liver, and fermented foods have vitamin K2 in them," he says. That way, you get all the benefits of those foods as well as the vitamins.