Genes May Affect Vitamin D Levels and Health
Study finds that variations in vitamin D metabolism genes could alter health outcomes
--by Alexia Severson
Variations in vitamin D metabolism genes could play a critical role in regulating the body’s vitamin D levels, and alter the risk of hip fracture, heart attack, cancer, and even death, according to a study appearing in the Nov. 14 issue of the Journal of the American Medical Association.
Vitamin D status is defined by the circulating concentration of 25-hydroxyvitamin D in the blood, which is the active form of vitamin D that helps control calcium and phosphate levels in the body. Low concentrations of serum 25-hydroxyvitamin D have been associated with a risk of developing chronic diseases and other negative health outcomes. But studies have shown that differences in vitamin D metabolism may alter the clinical consequences of measured serum 25-hydroxyvitamin D.
According to the Mayo Clinic, vitamin D aids in the absorption of calcium and helps form strong bones. It is “found in many dietary sources, such as fish, eggs, fortified milk, and cod liver oil. The sun also contributes significantly to the daily production of vitamin D, and as little as 10 minutes of exposure is thought to be enough to prevent deficiencies.”
The Expert Take
In this study, Gregory P. Levin, Ph.D., of the University of Washington, Seattle, and his colleagues investigated whether known relationships between serum 25-hydroxyvitamin D concentrations and certain diseases would differ according to common variation in 25-hydroxyvitamin D metabolism genes.
The team discovered one very small genetic variation—a single-nucleotide polymorphism (SNP) within the vitamin D receptor (VDR) gene—that significantly modified associations of low serum 25-hydroxyvitamin D concentrations with major the health outcomes of hip fracture, heart attack, cancer, and death over a long-term follow-up. An SNP occurs when two sequenced DNA fragments from different individuals contain a difference in a single nucleotide—a compound that forms the basic structural unit of DNA.
“These results suggest that individuals with specific 25-hydroxyvitamin D metabolism genotypes may be particularly susceptible to, or protected from, the potential adverse health effects of low vitamin D,” authors of the study said.
Researchers also said these findings could help to identify the clinically relevant effects of 25-hydroxyvitamin D metabolism genes, as well as contribute to a better understanding of the biological impact of genetic variation within the vitamin D receptor. But more research is still required.
“Evaluating the identified interactions in randomized clinical trials of vitamin D supplementation, when available, would help to assess the validity of our results and pave the way toward identifying individual patients who may benefit most from vitamin D interventions,” the authors said.
Source and Method
This study consisted of an examination of 141 SNPs in a group of 1,514 white participants from the community-based Cardiovascular Health Study. Participants had serum 25-hydroxyvitamin D measurements taken in 1992 and 1993, and were followed up for a median of 11 years, through 2006.
Replication meta-analyses were conducted across the independent, community-based U.S. Health, Aging, and Body Composition, Italian Invecchiare in Chianti, and Swedish Uppsala Longitudinal Study of Adult Men cohort studies.
noted, this study could lead to a better understanding of individuals’
specific vitamin D needs and help to pinpoint patients who would benefit
most from taking vitamin D supplements. But until more research
confirms this theory, it’s important to be aware of your vitamin D
status and to make sure you're not deficient.
Currently, there is no consensus on the vitamin D levels required for optimal health. However, guidelines from the Institute of Medicine have increased the recommended dietary allowance of vitamin D to 600 international units (IU) for people ages one through 70, and raised it to 800 IU for adults older than 70 to optimize bone health. The safe upper limit was also raised to 4,000 IUs. A vitamin D concentration of less than 20 nanograms per milliliter of blood is considered inadequate.
Causes of vitamin D deficiency include:
- A lack of dietary sources of vitamin D, including fish, fish oils, egg yolks, cheese, fortified milk, and beef liver.
- Limited exposure to sunlight
- Conditions such as Crohn's disease, cystic fibrosis, and celiac disease, which affect your intestines' ability to absorb vitamin D from the food you eat
Several studies have examined the health implications of vitamin D. In a study published in November 2012 in the American Journal of Obstetrics and Gynecology, researchers found that maternal supplementation with 2,000 and 4,000 IU of vitamin D per day during pregnancy improved maternal and neonatal vitamin D status.
Another study, published in the American Journal of Epidemiology in 2012, looked at the association between vitamin D and mortality in Asian populations. During follow-up, 793 subjects died, including 279 who died of cerebrovascular accident, 217 who died of cancer, and 200 who died of cardiovascular disease. However, the authors found no association between the cause-specific or all-cause mortality outcomes and low levels of vitamin D.
A study published in 2001 in The Lancet, looked at whether or not vitamin D supplementation or deficiency in infancy could affect the development of type 1 diabetes. Researchers associated vitamin D supplementation with a decreased frequency of type 1 diabetes when adjusted for neonatal, anthropometric, and social characteristics.