March 2010 Issue

Vitamin Has Heart Appeal — Studies Show Benefits of Increasing Daily D
By Jenna A. Bell, PhD, RD, CSSD
Today’s Dietitian
Vol. 12 No. 3 P. 20

Vitamin D is not just for bone health anymore. Recent research points to an array of benefits related to cardiovascular biomarkers, blood pressure, and a longer life, with many health professionals advocating for an increase in the recommended intake level, citing evidence of benefits and safety.

“Large population-based studies have provided a strong indication that vitamin D offers a myriad of health benefits, but more research is needed to show a causal relationship and determine optimal amounts for various conditions,” says Julie Upton, MS, RD, CSSD, a dietitian, journalist, and author. “The emerging research on vitamin D is important to pay attention to as we see how the results fare with future clinical trials.”

With all of the noise about vitamin D, your clients may not need to be convinced of its benefits, but they may have questions about how it works and how to get it in a healthful manner. Here are some evidence-based reasons to have a vitamin D chat with your clients the next time heart health is the topic du jour.

Improve CVD Biomarkers
High concentrations of parathyroid hormone (PTH) and low concentrations of vitamin D metabolites (25-hydroxyvitamin D [25(OH)D] and calcitriol) are relative newcomers to the pool of cardiovascular disease (CVD) biomarkers, which already includes triglycerides and the inflammation marker tumor necrosis factor. A recent study explored how vitamin D may improve these CVD risk markers, especially in combination with weight loss. The researchers found that 83 mcg/day of vitamin D at the very least won’t hinder weight-loss efforts and is also able to significantly improve several CVD biomarkers.1

The participants were 200 healthy overweight adults in a weight-loss program who also had low blood concentrations of vitamin D (30 nmol/L). Researchers conducted the double-blind study over a 12-month period. The treatment group received 83 mcg/day in supplement form while the control group received a placebo.

The good news was that average 25(OH)D and calcitriol concentrations increased in the treatment group by 55.5 nmol/L and 40 pmol/L, respectively (P < 0.001). The control group saw a smaller increase of 11.8 nmol/L and 9.3 pmol/L, respectively (P < 0.001), potentially due to weight loss alone. Also, blood PTH dropped more dramatically in the vitamin D group than in the placebo group (-26.5% compared with -18.7%; P = 0.014), as did triglycerides (-13.5% compared with +3%; P < 0.001) and the inflammation marker tumor necrosis factor-alpha (-10.2% compared with -3.2%; P = 0.049). Results were independent of factors for which the study authors controlled, including weight loss, fat mass, and sex.

Interestingly, vitamin D supplementation increased LDL cholesterol concentrations compared with the control group (+5.4% compared with -2.5%; P < 0.001). Perhaps the positive outweighs the negative, but mixed results are yet another reason to stay current with the research.

Hamper Hypertension
Vitamin D may be a key ally in the fight against high blood pressure in six ways: by protecting the kidneys, helping blood vessels dilate, preventing insulin resistance that leads to hypertension, suppressing the renin-angiotensin-aldosterone system from raising blood pressure, and preventing secondary hyperparathyroidism (the result of low vitamin D triggering the parathyroid gland to release calcium, thereby raising blood pressure) and via anti-inflammatory effects.2

In addition to the biologically feasible mechanisms of action listed here, emerging results from human trials have also shown benefits. Vitamin D modestly lowered diastolic blood pressure (-3.1 mmHg, 95% CI -5.5 to -0.6) in people with high blood pressure (BP > 140/90), according to a recent meta-analysis of eight randomized controlled trials by Witham et al in the Journal of Hypertension.

In general, clients who have both vitamin D deficiency and hypertension will see the greatest blood pressure-lowering benefits. Conversely, some studies show that those with normal blood pressure and adequate blood vitamin D do not experience blood pressure benefits.2

Vitamin D’s role in the renin-angiotensin-aldosterone system is one that most directly impacts blood pressure because low vitamin D will trigger it into action. By way of review, recall that the system is a series of reactions designed to help regulate blood pressure. When systolic blood pressure falls to 100 mmHg or lower, the kidneys release the enzyme renin into the bloodstream. Then renin separates angiotensin from angiotensinogen, a large protein that circulates in the bloodstream. Angiotensin-converting enzyme then separates angiotensin II from angiotensin I, which is relatively docile on its own. At this point, it is important to recall that angiotensin II is an active hormone that not only causes arteries to constrict, raising blood pressure, but also triggers the release of aldosterone, which causes the kidneys to retain sodium, get rid of potassium, retain water, and increase blood pressure.

Sun, Food, and Supplements
When answering clients’ questions, dietitians may be wise to present the three main ways to get enough vitamin D—dietary sources, safe sun exposure, and supplements—and then explore which methods may be most appropriate for their lifestyle.

Food sources of vitamin D include nutritious options such as fatty fish, sun-dried mushrooms, and egg yolks. RDs can also recommend possibilities from the growing list of fortified foods, including some varieties of milk (eg, soy, almond, rice, oat, cow), orange juice, soft spread, yogurt, and breakfast cereal.

Nutrition professionals should keep in mind that vitamin D is one vitamin for which supplementation may be a good idea, as it is not as widely available in foods. Also, some clients may not be able to get enough sun exposure year-round to obtain the recommended levels of vitamin D, whether because of geography or a choice to avoid the sun and the damaging UV exposure.

Getting five to 30 minutes of sun twice per week is one way to get enough vitamin D, according to 2007 research from Holick in The New England Journal of Medicine. Sun exposure should be on the face, arms, legs, or back without sunscreen and during the peak hours of 10 am to 3 pm. However, since UV radiation from the sun contributes to skin cancer, the  American Academy of Dermatology recommends getting the vitamin through food or supplement sources.

Are Current Recommendations Sufficient?
By current guidelines, children and most adults need 200 IU/day of vitamin D. However, some healthcare professionals, supported by strong emerging research, are calling for increases. Supporters of increasing the recommendation include experts such as influential nutrition researcher Walter Willett, DPH, MD, a professor of medicine at the Harvard School of Public Health, who, along with colleagues from around the world, has made an appeal to media, vitamin manufacturers, and policy makers to help improve vitamin D status.3

Results from a large meta-analysis of 18 randomized, controlled trials suggest that adults who take a daily supplement in the 400 to 830 IU range may decrease their risk of all-cause death.4 The current upper limit of vitamin D established by the Institute of Medicine is 2,000 IU for adults5, but some argue that significant research has emerged since this threshold was set more than a decade ago. More recent studies have shown that higher intakes of up to 10,000 IU are not necessarily harmful, but these trials were not long term.6

The bottom line is that there is a healthy amount of evidence behind the calls to raise the intake recommendations. Although there is more to learn, RDs have good reason to encourage clients with cardiovascular health concerns to increase their daily dose of D.

— Jenna A. Bell, PhD, RD, CSSD, is an author and nutrition communications consultant in Chicago.

 

Resource
National Institutes of Health Dietary Supplement Fact Sheet: Vitamin D, http://dietary-supplements.info.nih.gov/factsheets/vitamind.asp

 

References
1. Zittermann A, Frisch S, Berthold HK, et al. Vitamin D supplementation enhances the beneficial effects of weight loss on cardiovascular disease risk markers. Am J Clin Nutr. 2009;89(5):1321-1327.

2. Pilz S, Tomaschitz A, Ritz E, Pieber TR. Vitamin D status and arterial hypertension: A systematic review. Nat Rev Cardiol. 2009;6(10):621-630.

3. Vieth R, Bischoff-Ferrari H, Boucher BJ, et al. The urgent need to recommend an intake of vitamin D that is effective. Am J Clin Nutr. 2007;85(3):649-650.

4. Autier P, Gandini S. Vitamin D supplementation and total mortality: A meta-analysis of randomized controlled trials. Arch Intern Med. 2007;167(16):1730-1737.

5. National Academy of Sciences, Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, D.C.: National Academy Press; 1997.

6. Cranney A, Horsley T, O’Donnell S, et al. Effectiveness and safety of vitamin D in relation to bone health. Evid Rep Technol Assess (Full Rep). 2007;(158):1-235.

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