Are you getting your three weekly hits of vitamin D?

Five to 25 minutes in the sun, three times a week, with about a quarter of the body surface uncovered is what we should all be aiming for, health experts say.

That’s because without vitamin D, we risk depression, poor sleep, fatigue and weaker bones and muscles. To stock up on it in less sunny months of the year, it helps to consciously head out into the sunlight and expose not just your face, but also arms and legs.

Dermatologists say the general rule of thumb is that if your shade outside is shorter than you are tall, you’ll be producing enough vitamin D with the sun.

If you have a lighter skin type with blonde or brown hair, about 12 minutes in the sun should be enough, dermatologists say. Darker skin types will need a few minutes longer.

The body itself produces 80 to 90% of its vitamin D in the skin with the help of sunlight, and a deficiency of the nutrient is harmful to health.

Vitamin D helps the body absorb calcium, which is necessary for building and maintaining healthy bones. Researchers say it may also play a role in muscle function and the immune system.

Vitamin D supplements are often readily prescribed for infants, who are born with low vitamin D stores and are dependent on breast milk, sunlight or supplements as sources of vitamin D in the first few months of life. Doctors regularly also recommend vitamin D tablets for pregnant women.

However researchers say such pills are of no benefit to healthy, active adults, and excessive amounts can even cause headaches, nausea and kidney calcification.

If you feel that you may need a supplement, it’s important to first have the vitamin D level in your blood checked so that a doctor can tell you how much should be taken.