"In just four months highdoses of vitamin D reduce arterial stiffness in young overweightobese vitamindeficient but otherwise still healthy AfricanAmericans researchers say.    Rigid artery walls are an independent predictor of cardiovascular related disease and death and vitamin D deficiency appears to be a contributor says Dr. Yanbin Dong geneticist and cardiologist at the Georgia Prevention Institute at the Medical College of Georgia at Augusta University.    So researchers looked at baseline and again  weeks later in  AfricanAmericans ages   all of whom had some degree of arterial stiffness  taking varying doses of the vitamin best known for its role in bone health.    In what appears to be the first randomized trial of its kind they found that arterial stiffness was improved by vitamin D supplementation in a doseresponse manner in this population they write in the journal PLOS ONE.    Overweightobese blacks are at increased risk for vitamin D deficiency because darker skin absorbs less sunlight  the skin makes vitamin D in response to sun exposure  and fat tends to sequester vitamin D for no apparent purpose says Dong the studys corresponding author.    Participants taking  international units  more than six times the daily  IUs the Institute of Medicine currently recommends for most adults and children  received the most benefit says Dr. Anas Raed research resident in the MCG Department of Medicine and the studys first author.    The dose now considered the highest safe upper dose of the vitamin by the Institute of Medicine reduced arterial stiffness the most and the fastest . percent in four months. It significantly and rapidly reduced stiffness Raed says.    Two thousand IUs decreased stiffness by  percent in that timeframe. At  IUs arterial stiffness actually increased slightly  . percent  and the placebo group experienced a . percent increase in arterial stiffness over the timeframe.    They used the noninvasive gold standard pulse wave velocity to assess arterial stiffness. Reported measures were from the carotid artery in the neck to the femoral artery a major blood vessel which supplies the lower body with blood. The American Heart Association considers this the primary outcome measurement of arterial stiffness.    When the heart beats it generates a waveform and with a healthy heart and vasculature there are fewer and smaller waves. The test essentially measures the speed at which the blood is moving and in this case fast is not good Raed says.    When your arteries are more stiff you have higher pulse wave velocity which increases your risk of cardiometabolic disease in the future says Raed.    The varying doses as well as the placebo participants took were all packaged the same so neither they or the investigators knew which dose if any they were getting until the study was complete. Both placebo and supplements were given once monthly  rather than daily at home  at the GPI to ensure consistent compliance.    Dong was also corresponding author on a study published in  in the journal BioMed Central Obesity that showed in this same group of individuals both  and  IUs restored more desirable vitamin D blood levels of  nanograms per milliliter.    The  upperlimit dose restored healthy blood level quicker  by eight weeks  and was also better at suppressing parathyroid hormone which works against vitamin Ds efforts to improve bone health by absorbing calcium they reported.    While heart disease is the leading cause of death in the United States according to the Centers for Disease Control and Prevention blacks have higher rates of cardiovascular disease and death than whites and the disease tends to occur earlier in life. The authors write that arterial stiffness and vitamin D deficiency might be potential contributors.    While just how vitamin D is good for our arteries isnt completely understood it appears to impact blood vessel health in many ways. Laboratory studies have shown that mice missing a vitamin D receptor have higher activation of the reninangiotensinaldosterone system says Raed. Activation of this system increases blood vessel constriction which can contribute to arterial stiffness. Vitamin D also can suppress vascular smooth muscle cell proliferation activation of garbageeating macrophages and calcification formation all of which can thicken blood vessel walls and hinder flexibility. Vitamin D also reduces inflammation an underlying mechanism for obesity related development of coronary artery disease says Raed.    Now its time to do a largerscale study particularly in highrisk populations and follow participants progress for longer periods Dong and Raed say. A year would give us even more data and ideas Raed adds.    Dong notes that pulse wave velocity and blood pressure measures are complimentary but not interchangeable. We think maybe in the future when you go to your physician he or she might check your arterial stiffness as another indicator of how healthy you are Raed says.    There were no measurable differences in weight or blood pressure measurements over the week study period.    The Institute of Medicine currently recommends a daily intake of  IUs of vitamin D for those age  and older. For adolescents and adults they recommend  IUs as the upper daily limit  was a previous upper limit.    More than  percent of Americans the majority of whom spend their days indoors have vitamin D insufficiency or deficiency. Dong an expert in vitamin D and a professor in the MCG Department of Population Health Sciences says about  minutes daily in the young sun  between  a.m. and  p.m.  but before your skin starts to get pink is the best source of vitamin D.    Foods like milk milk products like cheese and yogurt fatty fish like mackerel and sardines some greens like kale and collards and fortified cereals also are good sources. The researchers say a vitamin D supplement is an inexpensive and safe option for most of us."