What happens if you do not have enough vitamin D?
If you do not have enough vitamin D, your body doesn’t absorb calcium in food. If the body does not absorb calcium from food, bones become a source of calcium. The body is always seeking the level it needs and takes calcium where it can get it. The result: loss of calcium from bone.
The average healthy person loses about 500 milligrams of calcium every day from bones and replaces it with the same amount of new calcium. When someone is vitamin D-deficient, calcium is not replaced adequately, which leads to weak and fragile bones.
How do you know if you’re vitamin D-deficient?
Measuring the form of vitamin D made in the liver, called 25-hydroxyvitamin D, is the best way to find out whether you are deficient. Ask your doctor if you should do this blood test.
Bone density tests measure how much calcium is in bones. Low bone density signals a condition called osteoporosis. Severe vitamin D deficiency can be a sign of osteomalacia (Greek lesson: soft bones). In children, severe vitamin D deficiency appears as rickets.
When is the best time to measure vitamin D?
Your lowest level is likely to be in the middle of winter. Measure then. If you start taking in sun or supplements, measure again two to three months later. It takes about that long to get to a steady level.
What foods have vitamin D?
Few foods contain vitamin D, unless it’s been added (adding nutrients to food is called fortification). Orange juice, milk, yogurt, and cereal are often fortified with vitamin D. Check labels. To minimize processing, many organic products are not fortified.
Vitamin D is naturally present in fish, especially fatty, oily fish like salmon. Choose wild over farmed when you can: A study showed farmed salmon had about 25% of the vitamin D content as wild salmon. You can also get vitamin D from fish liver oils.
It’s best to get nutrients through natural sources, but get it however you can.
How much vitamin D should you take?
If you’re not getting enough vitamin D from the sun or food, you can take pills, capsules, drops, and other forms of vitamin D. Many multivitamins contain vitamin D.
How much vitamin D you need depends on factors like age and health issues. Talk to your doctor. Celiac disease and other conditions associated with malabsorption of food make it difficult for the body to absorb nutrients. People with these conditions and who have had gastrointestinal tract surgeries need more vitamin D.
- For people over age 70, the daily recommendation is 800 IU (20 mcg).
- For people below age 70 it’s 600 IU (15 mcg).
These recommendations meet the bone health needs for most people. In most situations, taking more than 4,000 units per day is not recommended.
What’s the most important thing to know about vitamin D?
Vitamin D plays an important role in health but it’s just one vitamin people need. Simply taking vitamin D will not fix everything that might be wrong with your health.
A version of this story first appeared in the Columbia University Irving Medical Center Newsroom.
John Bilezikian, MD, is an attending physician at NewYork-Presbyterian/Columbia University Irving Medical Center. He is also the Dorothy L. and Daniel H. Silberberg Professor of Medicine at the Columbia University Vagelos College of Physicians & Surgeons, vice chair of the Department of Medicine for international education and research, chief emeritus of the Division of Endocrinology, and director emeritus of the Metabolic Bone Diseases Program at Columbia University Irving Medical Center.