Down to Your Bones

You may have been hearing or reading a lot about vitamin D lately, and wondering why it’s so important.

It has been suggested that vitamin D plays several roles in keeping you healthy, and there is concern that those who get insufficient amounts may be more likely to develop a variety of diseases. However, there’s not enough evidence to support the role of vitamin D in areas of health other than helping to develop and maintain strong bones.

Vitamin D is important for your bones because it allows you to absorb the calcium in your food and in your prenatal vitamins. Calcium is the primary mineral in bone and is needed particularly when you’re pregnant or breastfeeding to maintain your bones and help promote your baby’s bone development. No matter how much calcium you take in, you won’t absorb it without enough vitamin D.

Among the many studies looking for any relationship between insufficient amounts of vitamin D and the risk of illnesses other than weak bones are some noting that women who have low levels of vitamin D in their blood while they are pregnant may have a higher risk of developing gestational diabetes and preeclampsia, and having babies who are small for their gestational age. However, these studies do no show that low vitamin D levels actually cause pregnancy complications or affect the health of babies. Much more research is needed to find out which illness — if any — other than weak bones could be caused by not getting enough vitamin D.

While you can get calcium from many types of foods — especially dairy products and green leafy vegetables — it’s hard to get enough vitamin D just from the foods you eat. Vitamin D is available in a limited number of foods. It is added to some dairy products and some fruit juices and is naturally available in liver, egg yolks and salmon.

Your skin also makes vitamin D when exposed to sunlight. However, even though vitamin D is sometimes referred to as the “sunshine vitamin,” it is difficult to get enough vitamin D just through sun exposure. This is especially true if you live in an area farther north or have darker skin color. In addition, due to the understandable concern about developing skin cancer, more people are keeping their skin covered or using sunscreen when going outside. This also limits your ability to make enough vitamin D.

The Recommended Dietary Allowance (RDA) for vitamin D is 600 International Units (IU) for women from the age of 14 to 50, whether pregnant and breastfeeding or not. This is calculated based on an assumption that you have minimal exposure to sunlight and make little vitamin D on your own. However, more is not necessarily better and can be harmful, especially if you take more than 4,000 IU each day.

You can find out if you are getting enough vitamin D through a blood test. However, your healthcare provider most likely won’t recommend this test, unless you are at risk for low vitamin D levels (for example, if you are a vegetarian, vegan or lactose intolerant and don’t consume vitamin D-fortified dairy products; get limited or no sun exposure; or consistently cover your arms and legs or use sunscreen whenever you go outside). In addition, how vitamin D is handled in the body seems to be different during pregnancy. This has made it difficult to figure out what the level of vitamin D in your blood should be while you are pregnant or breastfeeding. Better defining this level remains an area of research.

Just as with other nutrients, read labels on your food and supplement packaging to see how much vitamin D they contain. Most single servings (for example, eight ounces of milk or yogurt or two or three slices of cheese) of fortified products contain about 100 IU of vitamin D. Most prenatal vitamins contain about 400 IU of vitamin D. While your body can only absorb a limited amount of calcium at any one time and you should spread out your intake of calcium throughout the day, there is no limit on how much vitamin D you absorb. You will absorb vitamin D whenever you consume it during the day and no matter how much you consume. Also, you don’t need to take in calcium and vitamin D at the same time for vitamin D to help you absorb calcium.

Unfortunately, there are no symptoms of low vitamin D levels in your blood until your bones become weak. Discuss with your provider how to make sure that you are getting the right amount of vitamin D every day — especially if you are at risk for not getting enough. You need to keep your bones strong and help your baby’s bones develop.

Kimberly Templeton, MD, is President of the American Medical Women’s Association (AMWA) and Professor of Orthopaedic Surgery at the University of Kansas Medical Center in Kansas City.