Don't Believe the Hype: Vitamin D Supplements Unlikely to Prevent Chest Infections

A new study claiming vitamin D may prevent colds and more serious chest infections generated a spate of news stories about the sunshine vitamin while mostly ignoring the study's weaknesses. Researchers at Queen Mary University of London analyzed 25 earlier studies looking at the effectiveness of vitamin D in preventing respiratory tract infections. In all, these studies included 11,321 people aged from a few months old to 95 years.Many news stories reported that the number of people who got a chest infection was 12 percent lower in the group taking a vitamin D supplement. What they didn’t include was the overall absolute risk reduction - the actual reduction - which was only 2 to 3 percent. Absolute risk is a helpful way of showing the real magnitude of benefit but it’s often left out of news stories.Another useful way of looking at numbers from studies like this one are how many people would need to take vitamin D for one chest infection to be prevented. The answer in this case is 33. If looking only at people who had very low levels of vitamin D in their body to begin with, four people would need to take the supplement to prevent one chest infection. Those numbers can help you decide if you think it’s worthwhile to take the supplement.Vitamin D is important for bone development and helps the body maintain the right amounts of minerals such as calcium and phosphorus. Doctors say a person with a blood vitamin D level of 25 nmol/L or less is considered to be deficient. The recommended daily amount of vitamin D is 600 international units of vitamin D if you are age 1 to 70 and 800 IU for people older than that.That doesn’t mean you need to take vitamin D every day, unless your doctor says so. The Food and Drug Administration says “vitamin D is not required in daily dietary intake,” because the vitamin can be stored in the liver and used when your supplies run low. The only patients for whom there is evidence that vitamin D supplementation is needed regularly are those at high risk of osteomalacia, a condition where the bones are weakened.One of the easiest ways to get vitamin D is by exposing bare skin to sunshine. It’s difficult to get vitamin D through food since foods that contain the vitamin, such as mackerel and salmon, do so in very small amounts.You don’t need to tan to get vitamin D and the amount of time in the sun varies depending on the color of your skin. People with darker skin need to spend longer in the sun for their skin cells to make the amount of vitamin D they need.  Continue reading...