When exposed to sunlight, your body manufactures vitamin D using a type of cholesterol. (Yes, even a certain amount of cholesterol is necessary for good health!) This is why vitamin D is often referred to as the sunshine vitamin. But unless you work outdoors or frequently engage in outdoor activities, it can be difficult for many to get enough vitamin D from sunlight. And few foods contain vitamin D—though some, like egg yolks, mushrooms, salmon, trout, sardines and fortified milk and juice, can be a good source.

If you don’t regularly nosh on those foods and you don’t get outside and expose yourself to the sun often enough, you might need a vitamin D supplement. A few common clues you could have a vitamin D deficiency include living in a northern climate, following a vegan diet, feeling depressed and having high blood pressure. 

In a study published on November 12 in the Journal of the Endocrine Society, researchers at the American University of Beirut Medical Center (AUBMC) in Beirut, Lebanon, honed in on the blood pressure-vitamin D connection. Here’s what they looked at and what they found.

How Was This Study Conducted?

There were 221 older individuals included in this study with an average age of 71 and an average BMI of 30. Just over half were women. 

Participants were randomly split up into two groups. One group took 600 IU/day of a vitamin D supplement (low-dose group) and the other group took 3,750 IU/day (high-dose group). In addition, all participants took 1,000 mg of calcium citrate a day. 

The study lasted one year. Baseline data was taken at the beginning of the study period, including age, sex, BMI, bloodwork—including vitamin D blood levels—blood pressure, heart rate and medical history. Participants attended clinical visits every 3 months, during which height, weight and vital signs (including blood pressure) were measured, questionnaires were filled out, supplement bottles were returned and refills were provided. Participants were also contacted by phone every 2 weeks to reinforce compliance with taking their supplements. Bloodwork was performed at the beginning of the study and then again after three months, six months and 12 months. 

What Did the Study Find?

After a year, all data was gathered and run through several statistical analyses. Researchers found that vitamin D supplementation was linked to a reduction in blood pressure. Specifically:

• Overall, across both groups, participants experienced a 3.5 mm Hg reduction in systolic (top number) blood pressure and a 2.8 mm Hg reduction in diastolic (bottom number) blood pressure. 
• On average, participants in the high-dose group experienced a 4.2 mm Hg reduction in systolic blood pressure and those in the low-dose group a 2.8 mm Hg reduction. 
• On average, participants in the high-dose group experienced a 3.02 mm Hg reduction in diastolic blood pressure and those in the low-dose a reduction of 2.6 mm Hg. 
• About the same number of participants from each group—approximately 42.5%—experienced a decrease in systolic blood pressure of 4 mm Hg or greater. And almost 46% of participants in both groups had a decrease in diastolic blood pressure of 2.5 mm Hg or greater.

Researchers also ran analyses on subgroups of participants to further refine results. “Our study found vitamin D supplementation may decrease blood pressure in specific subgroups such as older people, people with obesity and possibly those with low vitamin D levels,” said one of the study authors, Ghada El-Hajj Fuleihan, M.D., MPH, in a press release. “High vitamin D doses compared to the IOM’s recommended daily dose did not provide additional health benefits.”

How Does This Apply to Real Life?

Currently, the Institute of Medicine’s (IOM) recommendation for adults up to age 70 is a total of 600 IU (15 mcg) of vitamin D per day—the amount the low-dose group took. The IOM bumps this amount up after age 70 to 800 IU (20 mcg) per day. The recommended dosages for other age groups and conditions, like pregnancy, adolescents and children also vary.

There are a few things that are important to note regarding this study. First, participants were not taking just vitamin D. They were taking a combination of calcium citrate and vitamin D. So it’s difficult to say if the vitamin D supplement alone is what lowered blood pressure or if it was really the combination of the two—although those with lower vitamin D levels at baseline seemed to benefit more than those with normal serum vitamin D levels. There is evidence from previous studies suggesting that each on their own may reduce blood pressure. It may also be dependent on baseline blood levels of each—if you’re low in one or the other, supplementing and bringing your levels up to a normal range may be what helps reduce blood pressure.

Also, according to these researchers, the lower-dose group enjoyed about the same reductions in blood pressure as the higher-dose group. And because vitamin D is a fat-soluble vitamin, you can actually take too much of it, so more is not necessarily better. 

Researchers also noted that certain subgroups seemed to glean better results. This included those with a BMI over 30, people with high blood pressure and those with low vitamin D levels at baseline. And since the average age of participants was 71, we can’t say for certain if the same outcomes would apply to younger people. 

With that said, vitamin D and calcium are two nutrients that people tend to be low in. Do an assessment of your diet. Are you regularly eating foods high in vitamin D? What about calcium? Foods high in calcium include dairy—milk, cheese, yogurt—as well as canned sardines and salmon, white beans, fortified orange juice, soy milk, almond milk and tofu.

If you find that you’re short on these foods and would have a difficult time adding them into your diet due to food allergies, budget, food preferences or other reasons, you might want to consider supplementing. Before you do, ask your healthcare practitioner to test your blood levels of these nutrients to make sure that supplementing won’t put you well over the safe upper limit for them. Consider working with a registered dietitian to help find ways to incorporate foods rich in vitamin D and calcium and to help you find the best dose of each for you if you’re supplementing.

Regarding vitamin D, you also need to take into consideration your time spent outdoors. But not just time—the amount of exposed skin matters, too. Scientists recommend 5 to 30 minutes of unprotected sun exposure per day on the face, arms and legs, especially between 10 a.m. and 4 p.m. But certain factors can also influence how much vitamin D you get from the sun, including smog, cloudy conditions and skin color—darker skin tones tend to be less efficient at absorbing the sun’s UVB rays. There is some question regarding sunscreen and whether it decreases the body’s ability to produce vitamin D and more research needs to be done. And of course, you don’t want to risk frostbite during colder months to get your sunlight.

As far as blood pressure goes, calcium and vitamin D are not the only things to consider. The DASH diet is an eating pattern designed specifically to help lower blood pressure with lots of research to back it up. And other lifestyle habits influence blood pressure, too, including exercise, sleep, managing stressors, alcohol and smoking. 

The Bottom Line

This study suggests that supplementing with vitamin D and calcium citrate may lower blood pressure in older adults with high blood pressure, low vitamin D blood levels and/or a BMI over 30. While calcium is probably easier to get through food, vitamin D can be tricky and either nutrient might warrant supplementing. Have your blood levels checked and work with a registered dietitian to get the right amount for you. If you live in a climate conducive to exposing your skin to sunlight for a few minutes each day, go for it, since that will help your body make vitamin D. But even if you don’t, there are numerous other reasons to get outside every day—including reduced depression, stress and anxiety, and improved cognitive abilities, mood and sleep.