another link between vitamin d levels and cardiovascular health by floyd arthur (ppt)
TRANSCRIPT
Another Link Between Vitamin D Levels and Cardiovascular Health
By Floyd Arthur
Researchers at the Intermountain Medical Center Heart Institute in Salt Lake City,
Utah, have found a link between total and bioavailable vitamin D levels and
cardiovascular health. A team led by Dr. Heidi May, a cardiovascular epidemiologist at
the Institute, found that patients in whom both total vitamin D and bioavailable
vitamin D were low had the poorest cardiovascular outcomes.
Dr. May’s team measured the levels of various vitamin D metabolites in 4,200 patients
aged 52 to 76. Seventy percent of the study population had preexisting cardiovascular
disease, and about 25 percent had diabetes.
The research was presented at the American College of Cardiology Scientific Sessions in
Chicago, Illinois, held April 1 through April 4, 2016.
Vitamin D Levels and Cardiovascular Disease
A growing body of research links low vitamin D levels to a higher incidence of heart
attacks, peripheral arterial disease, congestive heart failure and stroke. Additionally,
low vitamin D levels are commonly linked to conditions associated with CVD, such as
obesity, hypertension and diabetes.
Only about 10 to 15 percent of total vitamin D in the body is available to pursue target
cells, Dr. May explains. The remaining metabolites are bound to proteins. Measuring
both total levels and bioavailable vitamin D appears to be important to determining
overall cardiovascular risk.
Predisposing Factors in Low Vitamin D Levels
“Vitamin D” is it is not a vitamin in the strict sense of the word. It is a fat-soluble
secosteroid produced in the skin from the action of ultraviolet light on 7-
dehydrocholesterol. Thus, low vitamin D levels are most often linked to decreased
exposure to UV light.
Over the past several decades the American population has spent more time indoors and
increased its use of sunscreen when outdoors in the sun. As a result, the incidence of low
vitamin D levels has increased.
Vitamin D can be obtained from dietary sources such as fish oils, egg yolk, butter, liver
and fortified foods. However, endogenous production is much more important to
maintaining vitamin D levels in most individuals.
Other important factors in vitamin D absorption include body weight, skin
pigmentation, sex and age.
* Fat cells absorb vitamin D, so obese individuals are more prone to vitamin D deficiency. This
correlation may explain the link between vitamin D deficiency and conditions associated
with obesity, such as Type 2 diabetes, CVD and hypertension.
* Fair skinned people absorb more vitamin D than those with darker skin due to lower levels
of melanin in the skin.
* Women have lower vitamin D levels than men. This may be due to the fact that women
generally have more body fat than men and traditionally spend more time indoors. Women
also tend to wear sun protection more often than men.
* The ability to absorb vitamin D decreases as people age, so people over 55 tend to have lower
levels of vitamin D. This effect may be intensified by the fact that older or medically frail
individuals tend to spend less time outdoors.
Additionally, those who live at higher latitudes tend to have lower levels of vitamin D
due to the decreased intensity of ultraviolet light.
What Are “Normal” Vitamin D Levels
Over the past several decades, optimal levels of vitamin D have been defined and
redefined. Historically, appropriate levels were determined by those found in healthy
populations, and so the lower end of the range was frequently set between 25 and 35
nmol/l. However, in the face of evidence linking levels below 50 nmol/l to greater all-
cause mortality, those numbers have been refined.
Today in the United States, the lower level of the reference range typically sits between
40 nmol/ and 120 nmol/l, with the majority of researchers suggesting that levels of 75
nmol/l are optimal. However, there are virtually no clinical trials supporting
supplementation for levels in this range.
Treating Low Vitamin D Levels
The logical clinical approach to treating suspected vitamin D deficiency is to measure
vitamin D levels and supplement those whose levels fall in the suboptimal range.
However, measuring vitamin D levels is expensive and inexact: Values from different
laboratories can vary by as much as 40 percent.
Thus, many clinicians choose to prescribe universal supplementation for persons in
“high-risk” groups, such as those who are elderly, medically frail, homebound or dark
skinned and living at higher latitudes. According to one study published in the Journal
of the American Geriatric Society, the cost-effectiveness of either approach in patients
65 to 80 is about the same.
If the clinician and patient choose supplementation, a dose of 500 to 1000 units per day
or 50,000 units per month are typically sufficient to achieve vitamin D levels of greater
than than 50 nmol/l. Some advocates of higher vitamin D levels suggest daily doses of
2,000 units, which will typically achieve levels of 100 nmol/l or higher. However, there
is some evidence that vitamin D levels above 120 lead to a greater incidence of falls and
fractures, so it is most likely safest to maintain levels at 100 nmol/l or below.
Conclusion
The relationship between low vitamin D levels and all-cause mortality is well-
established, and a growing body of research suggests a link between vitamin D
deficiency and cardiovascular risk. However, these correlations are confounded by
comorbidities that often exist in persons with low vitamin D, such as obesity, low
activity levels, dyslipidemia, hypertension and diabetes. More research is needed to
establish whether a causative relationship between low vitamin D levels and
cardiovascular disease actually exists.
