The test we're all forgetting to include in our yearly check-up.

I thought I was getting about as much sunshine as the average woman in her 40s. I don’t play sport, and I don’t tend to spend my days sunbathing in a bikini. But I do drop off and pick up my kids from school, and spend a bit of time hanging out with them in the backyard.

I assumed I was spending enough time in the sun to keep my vitamin D levels up. But last year, when my GP suggested I get my levels tested, I agreed. I was surprised to find I was a bit low.

Vitamin D is necessary for our bodies to be able to absorb calcium. It helps keep bones and teeth strong, and reduces the risk of osteoporosis. It also helps build muscle strength, and can boost immunity. It’s important for everyone to get enough vitamin D, but for women in our age group, it’s something we really need to keep in mind.

Vitamin D is found naturally in a few foods, including oily fish and eggs. As well, some foods are fortified with the vitamin. But most people only get a small amount from their diet.

The best natural source is the sun. Vitamin D is formed when skin is exposed to the sun’s UV radiation. But the amount of sunshine you should be getting to keep your levels up depends on a lot of different factors. So if you’re a fair-skinned Townsville woman, you’re not going to need much more than five minutes a day in the summer. But if you have darker skin, or live somewhere like Melbourne, you’re going to need more time – a lot more in the winter months.

The clothes you wear can also make a difference. If you tend to cover up when you go out, even with light shirts, you probably won’t be producing as much vitamin D as someone who gets around in singlet tops.

Age is another factor, and so is weight. Very overweight people are more likely to have a deficiency.

Obviously, you don’t want to get too much sun exposure, or you could be increasing your risk of skin cancer. It’s a matter of getting the balance right.

If you aren’t getting enough sun as part of your normal daily routine, a supplement is an option. Ostelin vitamin D supplements contain vitamin D3, the form produced naturally in the body.

To see whether you’re at risk of having low vitamin D levels, you can do the quick online Ostelin D-Test. A doctor can check your levels with a blood test and advise whether you need a supplement.

We all have a lot of health issues to think about as we get older. There are things like mammograms to schedule. On top of that, we often spend a lot of time worrying about other people’s health: our kids, our parents.

But we can’t forget about vitamin D.

Are you or someone you know affected by low vitamin D?