The researchers in Gothenburg studied the vitamin D levels, during different seasons, in 550 blood donors and found that, during the winter months, as many as half of them had insufficient levels of the vital vitamin.
These were healthy people, who were not aware of their low levels of vitamin D.
A lack of vitamin D can make you feel tired and without energy, and sometimes also depressed. It is an essential vitamin for your calcium balance, your skeletal health and your immune system. Recent studies have also shown a link between vitamin D deficiencies and certain diseases such as diabetes, MS, cardiovascular diseases and cancer - although it is still unsure if you can reduce the risk of these diseases by taking vitamin D.
The most important source of vitamin D comes from the body itself, where the skin - exposed to UVB light from the sun - will produce the vitamin by itself. But the problem for us here in the north is that the UVB rays are too weak and too far between in the winter.
Even the spring months, after the light has returned, are not much use to our vitamin D levels, as the UVB radiation is not strong enough. Even in April and May you will have to stay outdoors for pretty long for any vitamin D production to kick in.
This is the first bigger study in Sweden so far to measure the vitamin D levels, but it is in line with other studies in countries as far north as we are. Interestingly, the people in this study who were taking multi-vitamin supplements during the winter were not really helped in the vitamin D department. Probably, says Eva Klingberg, one of the researchers in the study, because the dose was to low.
The study did find that the vitamin D levels were higher among the people who had been on a holiday to the southern hemisphere during the winter, or people who used sun beds. But that is nothing that Eva Klingberg recommends: travelling far is not something everybody can afford, and anyway, it is not good for the environment, she says. And sun-beds may help you with the vitamin D levels, but they also increases your risk of getting skin cancer.
So what remains, is getting better at eating fatty fish, at least once a week in the winter, and maybe it could help taking extra vitamin D supplements - but for that several bigger studies are currently being made to see how much difference it can make, and what dose is the right one. The results of these studies are expected to be ready in a couple of years, according to Eva Klingberg, researcher at Sahlgrenska University Hospital in Gothenburg.