Vitamin D: The Other Nutrient Essential for Strong Bones
Most people are familiar with calcium’s role in bone health, but did you also know that without vitamin D, your body wouldn’t be able to absorb and effectively utilize calcium? For this reason, vitamin D plays an essential role in maintaining a healthy mineralized skeleton.
Research also suggests that vitamin D may help keep your immune system strong, reduce risk of high blood pressure, and regulate cell growth and differentiation, the process that determines what a cell is to become. Vitamin D is also necessary for maintaining normal blood levels of the mineral phosphorus.
Moreover, not getting enough vitamin D has been linked to osteoporosis — a condition that causes bone fractures and affects more than 10 million Americans and threatens 34 million. In children, vitamin D deficiency causes rickets. Rickets is a bone disease characterized by a failure to properly mineralize bone tissue. The most common causes of osteoporosis and rickets are vitamin D deficiency from a vitamin D deficient diet, lack of sunlight, or both. For older people, vitamin D deficiency is common because their skin cannot synthesize vitamin D as efficiently and the kidney is less able to convert vitamin D to its active hormone form.
Vitamin D is found in numerous dietary sources including fish, eggs, fortified milk, and cod liver oil. The sun is also a significant contributor to our daily production of vitamin D. However, in northern latitudes, particularly during the winter months (from November through February), it is not possible to get enough vitamin D from the sun. That is why it is extremely important for individuals with limited sun exposure to include good sources of vitamin D in their diet. In lower latitudes and during the rest of the year farther north, exposure to sunlight for just 10 – 15 minutes a few days a week followed by the application of sunscreen is adequate for vitamin D absorption.
Note that the term “vitamin D” refers to several different forms of this vitamin (that is, vitamin D is actually a group of fat-soluble prohormones). Two forms are important in humans: ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Vitamin D2 is synthesized by plants. Vitamin D3 is synthesized by humans in the skin when it is exposed to ultraviolet-B (UVB) rays from sunlight or the diet.
How much should you get? The Institute of Medicine recommends an adequate intake (AI) level of 5 micrograms (200 IU) daily for all individuals (males, female, pregnant/lactating women) under the age of 50 years-old, 10 micrograms daily (400 IU) for all individuals from 50 – 70 years-old, and 15 micrograms daily (600 IU) for those who are over the age of 70 years-old. The daily “upper limit” for vitamin D is 25 micrograms (1,000 IU) for infants up to 12 months of age and 50 micrograms (2,000 IU) for children, adults, pregnant, and lactating women due to toxicities that can occur when taken in higher doses.
- Modern Menus
Have questions regarding this article? Ask the Nutritionist.