It’s well known that vitamin D is required for strong bones. Yet, the more we learn about the “sunshine vitamin,” the more we see its widespread influence on many health systems outside of this traditional role.
A point of interest has been vitamin D’s function in cardiovascular health. More specifically, a growing number of studies have found that high plasma vitamin D levels are associated with a reduced risk of high blood pressure.
High blood pressure, or hypertension, has become known as the “silent killer” due to its ability to wreak havoc on your health while often showing no symptoms at all. According to the Centers for Disease Control and Prevention (CDC), in 2019, more than half a million deaths in the United States had hypertension as a primary or contributing cause.
What is High Blood Pressure?
As the heart beats, blood is pumped from the heart into the blood vessels and to the rest of the body. Blood pressure is the force of the blood pushing against the vessel walls.
Blood pressure is measured using two numbers. The first, or top number, is systolic blood pressure and it measures the pressure in your arteries when your heart contracts. The second, or bottom number, is diastolic blood pressure and it measures the pressure in your arteries when your heart is at rest.
High blood pressure happens when blood flows through the arteries at a higher-than-normal rate. The American Heart Association has an easy-to-read chart displaying “healthy” and “unhealthy” blood pressure ranges. Still, generally speaking, anything above 120/80 is considered higher than normal blood pressure. Many who develop high blood pressure do so in their late 30’s or 40’s. However, due to the rising number of children who are overweight or obese, we are seeing hypertension develop in more and more children.
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Blood pressure can change based on (1) the amount of blood your heart pumps or (2) the amount of resistance to blood flow present in your arteries. Therefore, it’s not uncommon for blood pressure to rise acutely during events throughout the day, such as a stressful situation or during exercise. The primary concern is chronically high blood pressure, or hypertension, that is most often due to narrowing arteries over time, causing resistance to blood flow.
Early detection and correction of high blood pressure are vital. Uncontrolled high blood pressure can increase your risk of severe health problems, including heart attack, stroke, congestive heart failure, peripheral artery disease, dementia, vision loss, and end-stage renal disease. Regularly measuring your blood pressure is the best way, and frequently the only way, to know where your blood pressure lies.
What is the Link Between Vitamin D and Blood Pressure?
Observational studies have noted geographic and racial differences in blood pressure and the prevalence of hypertension. Does this sound familiar? Similar to vitamin D deficiency trends, it has been recognized that hypertension is more prevalent during the cold months and is correlated with distance from the sun.
The INTERSALT study, which examined more than 10,000 participants worldwide, found that systolic and diastolic blood pressure was significantly and positively associated with distance from the equator. Correspondingly, latitude is a statistically significant risk factor for vitamin D deficiency. UVB light from the sun promotes the development of vitamin D in the skin. UVB light decreases in cold seasons and as you get further away from the equator, you get less vitamin D production.
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Also similar to vitamin D deficiency trends, hypertension is more prevalent in African Americans, with more than 40% of African Americans in the US experiencing hypertension while just 25% of Caucasian Americans do. Likewise, vitamin D deficiency is more prevalent among African Americans than other Americans since darker skin pigmentation reduces vitamin D production from UVB light.
Finally, one of the strongest correlations was revealed in a 1998 study when researchers utilized UVB light to treat patients who were vitamin D deficient and mildly hypertensive and found it decreased their blood pressure. The scientific community began to wonder if UV light intensity and efficiency of epidermal vitamin D synthesis may contribute to geographic and racial variability in blood pressure and the prevalence of hypertension.
How Might Vitamin D Influence Blood Pressure?
While a few mechanisms have been suggested, one seems to have the most scientific support, and it has to do with the renin-angiotensin system (RAS). The RAS plays an essential role in regulating blood pressure, electrolyte, and volume homeostasis in humans and animals. Inappropriate stimulation of the RAS has been associated with hypertension, heart attack, and stroke.
The first and rate-limiting component of the RAS cascade is renin. Studies have revealed an inverse relationship between plasma 1,25-dihydroxy-vitamin D concentration and plasma renin activity in both normotensive and hypertensive patients.
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Vitamin D has been found to repress renin expression in several ways. First, renin secretion by the kidney is inhibited by an increase in free intracellular calcium concentration. The increase in free intracellular calcium content may be amplified by serum 1,25-dihydroxy vitamin D. Additionally, vitamin D repression of renin is thought to act independently of calcium. In cell cultures, 1,25-dihydroxy vitamin D directly suppresses renin gene transcription by a vitamin D receptor (VDR)-dependent mechanism.
Furthermore, Angiotensin II (Ang II), a downstream product of the RAS, is a potent vasoconstrictor. Uncontrolled RAS activity will lead to increased levels of Ang II, which can lead to hypertension and cardiac hypertrophy development. Ang II also acts as a thirst-inducing agent and potent stimulator of intestinal sodium absorption, ultimately increasing blood pressure. Collectively, studies reveal that vitamin D can help regulate blood pressure and volume homeostasis by suppressing renin expression and influencing the RAS.
Does Research Confirm that Vitamin D Influences Blood Pressure?
The most convincing mechanistic studies linking vitamin D with RAS blood pressure regulation have been conducted in animal models. One study dove deep with VDR-null mice. They demonstrated that renin expression was more than 3-fold higher than that of wild-type littermates, and both systolic and diastolic blood pressures were significantly higher (>20mmHg) than those of wild-type littermates. Once these abnormal mice were treated with an angiotensin-converting enzyme inhibitor, blood pressure was reduced, confirming that the increase in blood pressure of the VDR-null mice was due to renin and RAS elevation.
To confirm that vitamin D indeed suppresses renin expression in vivo, the researchers treated the wild-type mice with vitamin D. They found that after two days of dosing with vitamin D that renal renin expression was decreased by 35%, and after five days, it was decreased by 50%, confirming the existence of a negative regulatory interaction between vitamin D and the RAS.
This study went a step further. Since vitamin D is a primary regulator of calcium homeostasis, changes in vitamin D status will inevitably alter blood levels of calcium and parathyroid hormone (PTH). Therefore, the researchers wanted to determine whether the effect of VDR inactivation on renin expression in vivo is direct or is secondary to changes in blood calcium or PTH levels.
They did this by treating the VDR-null mice with calcium until calcium levels normalized and found that renin and Ang II levels in the normocalcemic adult VDR-null mice were still significantly elevated. This finding confirms that elevation of renin expression is independent of hypocalcemia. Altogether, the researchers concluded that vitamin D functions as a negative endocrine regulator of the RAS and suggests that maintaining normal serum vitamin D levels is essential for maintaining blood pressure homeostasis.
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Several human studies have reported beneficial effects on blood pressure from vitamin D supplementation as well. In one study, scientists wanted to report the impact of taking a vitamin D supplement on the risk of hypertension in African Americans who had normal blood pressure.
Researchers provided two hundred fifty subjects with vitamin D at 1,000 IU per day, 2,000 IU per day, 4,000 IU per day, or a placebo for three months. They found that for every increase in vitamin D supplementation provided, systolic blood pressure declined, yet diastolic blood pressure remained the same.
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Another study in Denmark provided people with hypertension either 3,000 IU of vitamin D per day or a placebo for 20 weeks. They found that people in the supplementation group who were vitamin D deficient at baseline had significant decreases in systolic blood pressure compared to the placebo group.
A large meta-analysis confirmed these findings, observing that increased vitamin D concentrations were associated with decreased systolic blood pressure and reduced odds of hypertension, but with no effects on diastolic blood pressure.
However, not all research demonstrates a beneficial effect of vitamin D on blood pressure. A 2014 meta-analysis of randomized clinical trials did not reliably demonstrate a substantial causal effect of vitamin D status on blood pressure. Another meta-analysis found only weak evidence to support a small effect of vitamin D on blood pressure in studies of hypertensive patients.
Overall, evidence from clinical and epidemiological studies supports a possible relationship between low vitamin D levels and hypertension. Vitamin D screening should be included in patients presenting with hypertension. If vitamin D deficiency exists, correction may support improvement of hypertension. If vitamin D is sufficient, supplementation is not likely to help.
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Lastly, since hypertension is commonly multifactorial, it’s expected that other lifestyle factors such as smoking, obesity, and physical inactivity will likely need to be addressed to achieve optimal results.
Five things you can do to support your blood pressure:
- Shed those extra pounds. Blood pressure often increases as weight increases. Weight loss is one of the most effective lifestyle changes for controlling blood pressure if overweight or obese.
- Exercise regularly. The Mayo Clinic states that exercising about 30 min a day most days of the week can lower your blood pressure by 5-8 mmHg if you have high blood pressure. Consistency is key.
- Eat a healthy and balanced diet. If you have high blood pressure, both the Dietary Approaches to Stop Hypertension (DASH) diet and the Mediterranean diet have been found to reduce blood pressure and support longevity.
- Reduce your stress. Chronic stress can contribute to high blood pressure. Be sure to take time for yourself regularly, nourish supportive relationships with family and friends, and find a mental health care provider if necessary. Your life may depend on it.
- Test your vitamin D levels. Now that you better understand vitamin D’s role in managing blood pressure test your levels regularly to help you stay on track. Click here to find other articles that discuss vitamin D’s role in other aspects of health.