People should go outside and absorb some sunshine to help increase their vitamin D levels, some experts say. Arthritis Research UK. which is a British medical research organization dedicated to curing arthritis  , says vitamin D deficiency can cause bone loss, muscle function problems and, in some cases, rickets   in children. The government recommends vitamin D supplements   for pregnant women and children aged under five. But on sunny days, a few minutes outdoors should achieve the same results, Arthritis Research UK says. Figures show that up to a quarter of the population has low levels of vitamin D in their blood and the majority of pregnant women do not take vitamin D supplements. People aged over 65, pregnant and breast-feeding women and children aged six months to five years old are thought to be most at risk. Vitamin D is essential to help the body absorb calcium   from food. Low levels of vitamin D can result in serious problems. Alan Silman, the medical director of Arthritis Research UK, said, "When the days are sunny, go out for a few minutes and expose your face and arms to the sunshine." But he also had a warning on overexposure. "Don't allow your skin to go red, and take care not to burn, particularly in strong sunshine and if you have fair or sensitive skin. From June to August, just 15 minutes is generally enough time." "In less sunny months," Alan Silman added, "we recommend that people add more vitamin D in their diet by eating more oily fish such as salmon, tuna, and foods rich in vitamin D, such as cereals  ." Lack of vitamin D may cause the following problems EXCEPT   _  .
bone loss muscle function problems rickets in children. high blood pressure