Vitamin D and Calcium for Bone Health

Recently, we have been discussing bones, calcium and Vitamin D in many of my classes.  It was so interesting that I thought I would share some of the information with you in a couple of posts.

Some quick facts about bones:

• It is the framework for posture and movement of our body.
• It is primarily made of calcium and phosphorus (in addition to protein and some other nutrients). It is also a major reservoir for calcium; more than 99% of our body's calcium is stored in our bones.
• It is a living tissue with a number of different cells, blood vessels and nerves.
• It is constantly being broken down and then replaced - new bone is made and old bone is broken down (this process occurs in really really small portions of the bone). A delicate balance is always maintained between bone formation and bone loss. 
• When we are young, new bone is formed at a much faster rate than old bone is lost -  this helps us to grow.
• Our bones reach the maximum strength around the age of 25. But after a certain age, our bone loss becomes greater than new bone formation (more about this in the next post!).

But, why should there even be a bone loss, why not just continue building bones or stop building bones when it is not necessary?

This is where calcium comes in. We all probably know that calcium is very important for our bones. But what many of us don’t know is that calcium is also important for many other functions in our body. Our muscle requires calcium to work, our heart requires calcium to function, our nervous system requires calcium to send signals from the brain to rest of the body. This list goes on and on. These calcium dependent functions are so important for our survival that when our body doesn’t get enough calcium from the diet, bone is degraded and calcium stored in the bone is released. Our body makes absolutely sure that there is adequate calcium for these essential functions, even if it means breaking down bone. It is up to us to eat sufficient calcium so that calcium needs for the vital functions and bone formation, are met. When we don’t eat enough calcium, our bones become weak and are more prone to fractures and other problems.

In addition to calcium, Vitamin D, Vitamin B12, Vitamin K and proteins are also important for bone density and strength. After calcium, Vitamin D is probably the most important nutrient for bone health. It is highly essential for absorbing calcium from food. It also decreases calcium loss from our bodies - decreases excretion in the urine. No matter how much of calcium rich foods we eat, without Vitamin D, we cannot really absorb all that calcium. Optimum vitamin D level in our blood is 25nanogram/ml. At this level we can absorb nearly 90% of the calcium from our diets. If vitamin D levels are lower, then we absorb only 10-15% of calcium from our diets.

So it is really important to have adequate intake of calcium and adequate levels of Vitamin D for healthy, strong bones. 

The recommended intake levels of calcium for children and teenagers (age 9-18 years) is 1300mg/day, for adults (age 19-50 years) is 1000mg/day and for elderly (>50 years) is 1200 mg/day. I will talk more about why recommended intake levels vary for different age groups in my next post. Similarly for Vitamin D the recommended intake level  for children and adults (age 1-70 years) is 15 microgram/day and for elderly (>70 years) is 20 microgram/day.

These intake levels vary slightly if you are pregnant or breastfeeding. Please refer to this link (PDF file) if you want more information on adequate intake levels.

Some of the dietary sources of calcium include milk, other dairy products such as cheese and yogurt (1 cup of milk has about 300mg of Calcium), tofu made with calcium, sardines, canned salmon, a few greens such as kale, collard, mustard and beans such as pinto beans, red beans and white beans.

We synthesize vitamin D in our skin with the help of sun's rays. This is the primary source of vitamin D (Go out and get all the vitamin D you can while the sun is still shining!!!). Other dietary sources of Vitamin D include salmon, canned sardines, canned mackerel, Vitamin D fortified products such as milk, orange juice and cereal and egg yolks.

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Srilekha Karunanithi of Kirkland is a first-year Master's student in Nutritional Sciences at University of Washington who is training to become a Registered Dietitian. Her master’s program focuses on the influences of diet on health and how positive dietary changes help in the control and prevention of many diseases.