Vitamin D deficiency and heart disease
- Vitamin D Deficits May Affect Heart Health
Circulation, Volume 117, Number 4, January 29, 2008, pp. 503-511
What is the topic?
Vitamin D is an essential element that promotes bone growth, contributes to the immune system, and plays a role in a number of other cellular functions. Low levels of vitamin D have been associated with osteoporosis, type 2 diabetes, autoimmune diseases, and cardiovascular disease -- and it is estimated that one-third to one-half of all otherwise healthy middle-aged or elderly people have a vitamin D deficiency.
Vitamin D is usually obtained through exposure to sunlight, but can also be obtained through foods and in supplements. Fish is the only food source naturally rich in vitamin D, but certain foods (milk, soy, cereals) are often fortified with vitamin D, and can boost a person’s daily intake.
What did the researchers hope to learn?
Several studies have pointed to a link between vitamin D deficiency and cardiovascular disease (atherosclerosis, or "hardening of the arteries," which leads to risk for heart attack and stroke). However, it is still not clear whether vitamin D deficiency is a cause or a consequence of cardiovascular disease. In this study, the researchers hoped to establish more definitely the relationship between vitamin D levels and cardiovascular disease. Although this study is not specifically about lupus, it may be important information for people with lupus, given the risk factors for heart disease reviewed above (see previous articles, "Accumulation of coronary artery disease risk factors over three years ..." and "Recent corticosteroid use and recent disease activity: Independent determinants ...").
Who was studied?
This research involved 1,739 individuals who were participants in an ongoing observational study in Massachusetts. All of the participants were Caucasian, and 55% were women. The average age was 59 years. The researchers did not enroll anyone into the study who had a previous history of cardiovascular or kidney disease; by eliminating these risk factors, it was possible to focus on more of the underlying factors that may create long-term risk over a lifetime, starting when people are relatively young and healthy.
How was the study conducted?
At enrollment each of the participants underwent a physical examination, medical history, and tests for cardiovascular risk factors (high blood pressure, cholesterol, type 2 diabetes/high blood sugar, body-mass index (BMI), physical activity, and smoking). The level of vitamin D in participants’ blood samples was also measured. (The test to measure vitamin D, called 25-OH D, reflects the total, fully active vitamin D from both diet and the effects of sunlight.) Less than 15 ng/mL (nannograms per milliliter) suggested a vitamin D-deficiency, and levels below 10 ng/mL were a sign of severe deficiency. The average level among participants at their first visit was 19.7 ng.mL. Of the 1,739 participants, 28% were vitamin D-deficient (25-OH D<15 ng/mL), and 9% were severely deficient (25-OH D<15 ng/mL).
Participants were followed on average 5.4 years (maximum follow-up was 7.6 years). Over the course of the study, 120 participants had their first cardiovascular event—either angina (chest pains), heart attack, coronary insufficiency (diminished blood supply to the heart), stroke, TIA (transient ischemic attack, also called a "ministroke"), claudication (leg pain from restricted blood flow), or heart failure.
Using statistical methods to adjust for other risk factors, the researchers compared the cardiovascular outcomes of the participants with and without vitamin D deficiency. They also analyzed those groups based on whether or not the participants had high blood pressure (hypertension), since vitamin D has been linked to blood pressure.
What did the researchers find?
The 5-year rate of cardiovascular disease was approximately twice as high in participants with vitamin D deficiency (25-OH D<15 ng/mL) as in those with 25-OH D levels above 15ng/mL. The highest rate of cardiovascular disease was found in those participants who had both high blood pressure and vitamin D deficiency.
When adjusted for conventional risk factors, vitamin D deficiency increased the risk of developing cardiovascular disease by 63% in those who had hypertension, and the risk was increased when the vitamin deficiency was severe. Interestingly, vitamin D deficiency did not increase the risk when there was no hypertension.
What were the limitations of the study?
The researchers chose 25-OH D<15 ng/mL as the cut-off for vitamin D deficiency. However, a 25-OH D level of 30ng/mL is recommended for bone health, but only 10 percent of the study population had levels that high.
Vitamin D levels can be altered through the use of supplements, dietary changes, or increased outdoor activity that allows more exposure to sunlight; this study did not analyze the causes of any changes in a participant’s vitamin D status over time.
Since all the participants were Caucasian, it is not certain that the associations between hypertension, vitamin D, and cardiovascular disease shown here would hold among other ethnic groups. Further studies with a more ethnically diverse study population are needed for this to be determined.
What do the results mean for you?
People with lupus are advised to avoid sunlight because exposure to ultraviolet light can contribute to flares. Staying out of the sun, however, raises the risks that they can become vitamin D deficient. Therefore, it might be advisable for lupus patients to have their vitamin D levels checked regularly, and to make adequate vitamin D levels an integral part of their preventive health program. This is also very important because steroids can cause severe osteoporosis, and adequate vitamin D is critical to maintaining strong bones.