Without vitamin D, your bones may not grow strong at any age. Why? Because for your bones to make the best use of calcium, they need  vitamin D, says Robert P. Heaney, MD, researcher and professor in the Osteoporosis Research Center at Creighton University.

But did you know that even mild shortages of vitamin D can contribute to diabetes, some cancers, high blood pressure, heart disease, and pregnancy problems? “Asking the body to deal with these disorders without adequate vitamin D is like asking a fighter to enter battle with one hand tied behind his back,” said Dr. Heaney. Vitamin D is a chemical that our body’s tissues use to produce biochemical products required for daily life. It’s less important to understand the process. It’s more important to know where to get vitamin D and how much you need.

Some Facts

•  Your skin produces vitamin D when you are exposed to certain rays of the sun. If you never get sunshine on your skin, you will not get enough ultraviolet radiation for your skin to make vitamin D.

•  Sunlight in winter in most of the U.S. is so weak, it does not allow you to produce enough vitamin D, even if you’re outside in winter during midday.

•  During summer months, a light-skinned person wearing a bathing suit will make about 15,000 IU of vitamin D in 15 to 20 minutes. Darker-skinned people can do the same, but it will take twice as long.

•  Sunscreen blocks the radiation and prevents your skin from making vitamin D. Brief sun exposure, said Dr. Heaney, is not enough to cause skin cancer. He suggested you apply sunscreen after the first 15 minutes in the sun.

•  Some food has vitamin D but not much. Vitamin D is added to many foods such as milk, some yogurts and orange juices, cheese, and breakfast cereals. Read the labels to see how much.

•  Because most of us do not get enough sun exposure (or choose not to) or enough vitamin D in food, Dr. Heaney suggests taking supplements of vitamin D3, the natural form. The label should say cholecalciferol (vitamin D3) or ask the pharmacist which supplement is best.

•  Vitamin D is safe to take. You may take supplements daily, weekly, or monthly. The important point is that you need to maintain a high enough blood level of vitamin D. This is measured by a blood test.

•  Dr. Heaney recommends, based on his research, that adults take supplements providing from 1,000 to 3,000 IU per day. This number is higher than the 600 to 800 IU Recommended Dietary Allowance per day. Follow your doctor’s advice for vitamin D.

•  Talk with your doctor about testing your blood level and discussing how much supplementation you may need in both summer and winter.