Dialing in on "D"eficiency

To better understand normal and deficient vitamin D levels, researchers studied the relationship between a hormone (parathyroid) and vitamin D in African American and white 50-to-79-year-old adults. Parathyroid hormone is produced in the body to help regulate calcium balance, and as vitamin D levels go up, parathyroid hormone levels go down.

The bottom of the normal vitamin D range is considered the level above which parathyroid hormone levels cannot be lowered any further. Current guidelines set this number at 30 ng per ml, meaning a person would not be considered low in vitamin D until his or her blood level dropped below 30 ng per ml.

The study suggests the "normal" vitamin D level may be different for African Americans and whites.

• For African Americans, parathyroid hormone levels began to go up--indicating that vitamin D levels were entering the deficient range--when D levels fell below 15 ng per ml, well below the 30 ng per ml value currently set as the lowest "normal" vitamin D value.
• For African Americans, parathyroid hormone levels stabilized between 19 and 23 ng per ml blood vitamin D levels.
• For white people, parathyroid hormone levels stabilized when vitamin D levels were greater than 32 ng per ml.

In other words, adequate vitamin D blood levels may begin around 20 ng per ml for African Americans, and around 30 ng per ml for whites.

What's normal for you?

This study suggests current optimal or "normal" vitamin D levels in whites may not be applicable to African Americans, or black people from any location. This is important: for African Americans, one study even suggests harm with higher vitamin D levels. Among 340 African Americans with type 2 diabetes, those with the highest D levels were more likely to have plaque build up in their arteries, a risk factor for heart attack and stroke. That study's author, Dr. Barry Freedman pointed out, "We need to determine whether we should be targeting the same vitamin D level in blacks as whites, and better understand the cardiovascular effects of supplementing vitamin D in African-Americans."

In the meantime

Here are some tips to guide your vitamin "D"ecisions:

• Master moderation. The Institute of Medicine sets a safe upper limit for vitamin D of 4,000 IU per day, and it's wise not to exceed this number.
• Add it up. Food sources of vitamin D include milk, fortified cereals and juices, and fatty fish, such as salmon. Consider this before adding supplements.
• Consider sun. If you live in a sunny, warm area, or get plenty of sun in the summertime regardless of where you live, you are likely making vitamin D. A supplement may be unnecessary in this situation.
• Ask the expert. If you have questions about whether you are getting enough, or even too much vitamin D, talk to your healthcare provider. He or she can offer guidance, taking into account your current lifestyle and nutritional needs.

(Osteoporos Int 2012; 23:2283-91; J Clin Endocrinol Metab 2010; 95:76-83)