In a matter of four months only, large doses of vitamin D were able to reduce arterial stiffness in young, overweight but otherwise healthy Afro-Americans, according to a study from Georgia, the United States. The study also showed that those participants, who only took the officially recommended quantities of vitamin D, had increased arterial stiffness. This suggests that the official vitamin D recommendations are too low to prevent stiff arteries and atherosclerosis. Another thing is that dark-skinned people living at northern latitudes, overweight individuals, older people diabetics, and those who overuse sun screen are at increased risk of synthesizing too little vitamin D.
Arteries are elastic blood vessels that lead the arterial (oxygenated) blood from the heart to the different tissues in the body. The pulsating contractions of the heart cause the blood to flow in spurts. Our blood vessels must therefore be able to adapt to this suddenly increased blood volume. The elasticity of the vessels also helps to even out the bloodstream, so that the blood is not limited to only flow during each contraction (systole).
Atherosclerosis and the ageing process may cause arterial stiffness. Sooner or later, the increasing atherosclerosis may lead to a host of different symptoms caused by impaired blood flow and, in worst case, result in heart infarction and stroke, which are leading causes of death in the Western world. Vitamin D holds great potential in the prevention of both atherosclerosis and arterial stiffness, provided you get an amount that is sufficiently high to benefit the cardiovascular system and heart.
Dark skin and overweight is an unfortunate combination
The researchers from Augusta University in Georgia studied 70 Afro-Americans aged 13-45 years, who all had some degree of arterial stiffness. The study participants were divided in four groups that were asked to take different quantities of vitamin D, a nutrient that is primarily known for its role in bone health.
The scientists say that this placebo-controlled, randomized study is the first to show that large doses of vitamin D (intended for this population group) can improve arterial stiffness. Professor Yanbin Dong, who headed the study, says that overweight Afro-Americans have an increased risk of lacking vitamin D. Firstly, dark-skinned people do not synthesize vitamin D in their skin to the same extent as people with light skin. Secondly, excess fat isolates (retains) vitamin D and prevents it from being converted to its active form in the blood.
|When UVB rays from sunlight reach our skin, they react with circulating cholesterol and synthesize a precursor of vitamin D. Vitamin D is then stored in the liver as 25-hydroxy-vitamin. When needed, the vitamin D is then converted in the kidneys into an active form called 1,25-D. Dark skin, impaired liver and kidney function and overweight may increase the need for vitamin D.|
The study participants were divided into four groups that got the following vitamin D doses for a period of four months:
- 100 micrograms
- 50 micrograms
- 15 micrograms
- Placebo (dummy pill without vitamin D)
Institute of Medicine in the United States recommends 15 micrograms of vitamin D daily to the majority of adults. This means that the group that got 100 micrograms of vitamin D took a daily dose that is 6.6 times larger than the official recommendations. According to the American health authorities and the European Food Safety Authority (EFSA), 100 micrograms of vitamin D daily is the upper safe intake level. However, a human can synthesize even more than that on a hot summer day, especially if that person has light skin.
The more vitamin D, the less arterial stiffness
During the four-month course, the study revealed that:
- The group that took 100 micrograms of vitamin D daily had the largest and most rapid effect on arterial stiffness (corresponding to a statistically significant 10.4 percent reduction)
- The group that took 50 micrograms of vitamin D daily had a two percent reduction in arterial stiffness
- The group that took 15 micrograms of vitamin D daily actually had a one percent increase in arterial stiffness
- The group that took placebo experienced a 2.3 percent increase in arterial stiffness
In order to assess the level of arterial stiffness, the researchers measured the pulse wave velocity in the carotid artery and the femoral artery. The constant throbbing of the heart generates a waveform that helps the blood circulate. If the heart and cardiovascular system are healthy, there are fewer and smaller waves. However, as arteries become increasingly stiff, the pulse wave velocity increases. This may eventually increase the risk of elevated blood pressure and other cardiovascular diseases.
As mentioned earlier, atherosclerosis is the leading cause of death in the United States, and the dark-skinned segment of the population is at increased risk of atherosclerosis and early death.
According to the scientists, being vitamin D-deficient may be a contributing cause. The study is described in PLoS ONE 2017.
|Atherosclerosis causes the arteries to become stiff and lose their elasticity. As a result of this, the heart has to work harder, and that makes the blood pressure go up.|
Vitamin D protects in several different ways
The researchers still do not know exactly how vitamin D protects against arterial stiffness and atherosclerosis, but there seems to be three mechanisms of action:
- Vitamin D reduces blood vessel constriction. According to laboratory studies, mice that lack vitamin D receptors (VDR) and are therefore unable to get enough vitamin D into their cells have an increased activation of the renin-angiotensin-adolsterone system that increases blood vessel constriction
- Vitamin D reduces the activity of the macrophages - the immune system’s “garbage collectors” – and their conversion into cholesterol-containing foam cells that become embedded in the arterial walls.
- Vitamin D reduces inflammation that is an underlying mechanism in overweight and cardiovascular disease.
Vitamin D and targeted supplementation in the future
According to researchers, Professor Yanbin Dong and Anas Read from Augusta University of Georgia, it is time to conduct larger studies of vitamin D, with particular focus on those population groups that have the greatest risk of deficiencies. The researchers plan to monitor these groups for extended lengths of time.
The researchers also assume that, in the future, doctors will be able to measure arterial stiffness and use it as an indicator of health and atherosclerosis.
More than 80 percent of Americans lack vitamin D, including those people who spend a lot of time indoors.
Professor Yanbin Dong says that the sun is the best source of vitamin D. In order for us humans to produce enough vitamin D, we need to spend at least 15 minutes in the sun every day between 10 in the morning and two in the afternoon. It is necessary, though, to avoid reddening and burning of the skin. At northern latitudes, it is not possible to synthesize vitamin D during the winter period, as the sun sits too low in the sky.
Your diet only provides minimal amounts of vitamin D – so supplements are necessary
You get vitamin D from cod liver, oily fish, and cod roe. There are also small amounts of the nutrient in avocado and dairy products. A minority of people get the recommended daily amount from their diets, and it is virtually impossible to get the large quantities that were used in the study. Therefore, vitamin D supplements are obvious as an effective and inexpensive way to take good care of your cardiovascular system. Vitamin D is lipid-soluble, which means that we are best able to utilize it when the vitamin is dissolved in some sort of oil in capsules.
Anas Raed et al. Dose responses of vitamin D3 supplementation on arterial stiffness in overweight African Americans: A placebo controlled randomized trial. PLOS ONE, 2017
Steen Ahrenkiel. D-vitamin behov og mangel i Danmark. Biokemisk forskning 2009
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