Quick Answer
There is some evidence that vitamin C may help lower blood pressure, especially when taken in high doses. However, the effect appears modest and more research is needed. Vitamin C supplements are unlikely to replace blood pressure medications, but may provide added benefit when taken alongside them.
What is vitamin C?
Vitamin C, also known as ascorbic acid, is an essential water-soluble vitamin. It acts as an antioxidant in the body and is important for many functions, including immune health, collagen production, and absorption of iron.
Good food sources of vitamin C include:
- Citrus fruits like oranges and grapefruit
- Strawberries, raspberries, blueberries, cranberries
- Peppers
- Broccoli
- Brussels sprouts
- Potatoes
- Tomatoes
The recommended daily intake of vitamin C is:
- 75 mg for women
- 90 mg for men
Smokers may require an additional 35 mg per day due to increased oxidative stress.
Vitamin C and blood pressure
High blood pressure, also known as hypertension, is a major risk factor for heart disease, stroke, and kidney failure. Lifestyle changes like losing weight, reducing salt intake, exercising, and managing stress are recommended first-line treatments, but many people also require medication to lower their blood pressure.
Research on whether vitamin C supplements affect blood pressure has shown mixed results:
Observational studies
Some observational studies have found associations between higher vitamin C intake from foods and lower blood pressure levels or reduced risk of high blood pressure. However, these types of studies cannot prove cause and effect.
Clinical trials
Results from clinical trials investigating vitamin C supplements and blood pressure have been inconsistent:
- Some small studies have shown modest blood pressure reductions with vitamin C supplements in the range of 4-5 mm Hg systolic and 1-2 mm Hg diastolic pressure.
- Other trials found no significant effect on blood pressure.
- A few studies found vitamin C lowered blood pressure specifically when participants were overweight, obese, or had existing high blood pressure.
In general, larger studies and meta-analyses (which combine data from multiple studies) have found that vitamin C supplements at doses under 500 mg per day have little or no effect on blood pressure in the general population.
However, there is stronger evidence that large doses of vitamin C, around 500 mg per day or higher, can lower blood pressure, especially in those with high blood pressure or other risk factors.
For example, one meta-analysis of 29 clinical trials concluded that vitamin C supplements at a median dose of 500 mg/day reduced systolic blood pressure by 3.8 mm Hg and diastolic blood pressure by 1.5 mm Hg compared to placebo. Larger blood pressure reductions of 4.9 mm Hg systolic and 1.7 mm Hg diastolic were seen in studies with higher vitamin C doses.
Another review found that doses of vitamin C at 500 mg/day or more lowered systolic and diastolic blood pressure by about 4 and 1.5 mm Hg, respectively. The blood pressure lowering effect was greater in people with existing high blood pressure.
Overall, there appears to be a dose-response relationship, with higher vitamin C intakes progressively lowering blood pressure more. But the effect is modest, even at high supplemental doses.
How vitamin C may lower blood pressure
Researchers aren’t entirely sure why vitamin C supplements may help lower blood pressure, but some of the proposed mechanisms include:
- Improving endothelial function. The endothelium is the lining of blood vessels. Dysfunction of the endothelial cells is thought to play a role in hypertension. Vitamin C may improve nitric oxide signaling and help relax and dilate blood vessels.
- Lowering oxidative stress. Oxidative damage is involved in hypertension. The antioxidant properties of vitamin C reduce reactive oxygen species and decrease oxidative damage.
- Decreasing plasma angiotensin converting enzyme (ACE) activity. ACE leads to constriction of blood vessels. Vitamin C may aid blood pressure reduction by decreasing plasma ACE activity.
- Improving insulin sensitivity. Insulin resistance is associated with increased risk of hypertension. By improving insulin sensitivity, vitamin C may have beneficial effects on blood pressure.
However, the effects of vitamin C in the body are complex, and other mechanisms are likely involved too. More research is needed to fully understand how vitamin C interacts with blood pressure regulation.
Benefits
Potential benefits of taking vitamin C supplements for blood pressure include:
- Modest reductions in systolic and diastolic blood pressure, especially at doses of 500 mg per day or higher.
- Greater blood pressure lowering effects in people with hypertension or other high-risk factors like obesity, smoking, high cholesterol.
- Well tolerated with low risk of side effects.
- Easy to obtain and inexpensive.
- Antioxidant effects may provide other health benefits like reducing oxidative stress.
While vitamin C alone is unlikely to replace blood pressure medications, it may provide added benefit when taken alongside them. Even a modest reduction in blood pressure of a few mm Hg can reduce the risk of cardiovascular events like heart attack and stroke.
Recommended dosage
There is no established recommended dosage of vitamin C specifically for blood pressure. Clinical studies have used varying doses, but benefits for blood pressure have been most consistently seen with:
- 500-1000 mg per day
- Up to 2000 mg per day in divided doses
It’s best to take vitamin C supplements with food to avoid stomach upset, especially at higher doses. Vitamin C is water soluble and does not get stored in the body, so it’s generally safe at high intakes. However, too much vitamin C may cause diarrhea, nausea, cramps or other gastrointestinal effects.
Talk to your doctor before taking high dose vitamin C supplements, especially if you have any underlying health conditions or take any medications. Very high doses above 2000 mg per day are not recommended unless medically supervised.
Risks and side effects
Vitamin C is considered very safe at the recommended daily intakes and at supplemental doses under 2000 mg per day. Possible side effects may include:
- Diarrhea
- Nausea
- Abdominal cramps
- Heartburn
- Headache
- Insomnia
High dose vitamin C could potentially worsen conditions like:
- Kidney stones
- Hemochromatosis (excess iron absorption)
- G6PD deficiency
Vitamin C may also interact with some medications including:
- Blood thinners like warfarin – vitamin C may raise INR levels
- Estrogen-containing contraceptives – vitamin C may increase estrogen levels
- Statins – vitamin C may lower statin effectiveness
- Blood pressure lowering medications – vitamin C may enhance the effect
Talk to your doctor before taking vitamin C supplements if you have any medical conditions or take any medications.
Food sources vs. supplements
It’s best to meet vitamin C needs primarily through food sources like fruits and vegetables rather than relying on supplements. However, to reach the 500-2000 mg/day range that may lower blood pressure, supplementation is likely needed in addition to dietary intake.
Advantages of getting vitamin C from foods:
- Less risk of adverse effects
- More health benefits from consuming whole foods
Reasons supplements may be useful:
- Easy to take high therapeutic doses
- Helps ensure consistent daily intake
For blood pressure benefits, vitamin C from both foods and supplements may be helpful. Eating plenty of vitamin C-rich foods provides antioxidant protection and other beneficial compounds, while supplements can provide the high doses that may specifically help lower blood pressure.
Other complementary supplements
Some other supplements that may help lower blood pressure include:
- Potassium: Potassium helps balance sodium levels and relax blood vessels. Supplemental doses of 500-2000 mg per day may help reduce blood pressure, especially for those with already high levels.
- Magnesium: Magnesium relaxes blood vessels and plays a role in regulating blood pressure. Doses of 350-500 mg per day have been linked to modest reductions in blood pressure.
- Calcium: Some research shows 1000-1500 mg/day of calcium supplements may lead to small decreases in blood pressure.
- Omega-3 fatty acids: The omega-3 fats in fish oil and flaxseed oil appear to have a small, dose-dependent blood pressure lowering effect.
- Garlic: Some studies suggest garlic supplements containing 1200-1500 mg per day may reduce blood pressure slightly.
Combining vitamin C with other beneficial supplements like these may have an additive effect for lowering blood pressure. However, more research is still needed.
Lifestyle changes
Vitamin C supplementation should always be combined with lifestyle changes to effectively reduce high blood pressure. Important lifestyle factors include:
- Losing excess weight
- Eating a healthy diet rich in fruits, vegetables, whole grains, lean protein
- Reducing sodium intake
- Exercising regularly
- Quitting smoking
- Cutting back on alcohol
- Managing stress through techniques like meditation, yoga, mindfulness
Adopting healthy lifestyle habits can help lower blood pressure and reduce the risks of heart disease, stroke and other complications.
Monitoring your blood pressure
It’s important to follow your blood pressure and have it checked regularly by a healthcare professional if you have hypertension. You can also monitor it at home between appointments.
Tips for at-home monitoring:
- Use a validated, upper-arm cuff monitor
- Take readings at the same time daily
- Sit quietly for 5 minutes before measuring
- Take 2-3 readings each time and record the average
- Bring your readings to doctor visits
Home monitoring provides more data points on your blood pressure than occasional office visits. This allows you and your doctor to better assess treatment effectiveness.
When to see your doctor
Consult your doctor before beginning vitamin C supplements, especially if you:
- Have hypertension
- Take blood pressure medications
- Are pregnant or breastfeeding
- Have kidney stones or kidney disorders
- Have iron overload
- Take estrogen contraceptives, blood thinners, or statins
See your doctor immediately if your blood pressure remains very high after starting vitamin C. Sudden very high blood pressure needs urgent medical care.
Schedule an appointment if your blood pressure is not lowering as expected with vitamin C supplements and lifestyle changes. Your medication dosages may need adjustment.
Conclusion
In summary, there is some evidence vitamin C supplements may help lower blood pressure, particularly at higher doses of 500-2000 mg per day. However, the effect appears small and more research is still needed.
Vitamin C supplements may provide added benefit when taken alongside blood pressure medications, but should not replace medication. Getting adequate vitamin C from foods like fruits and vegetables is recommended for overall health.
To effectively manage high blood pressure, vitamin C supplementation should be combined with a healthy lifestyle including weight loss, sodium reduction, exercise, stress management, and avoiding smoking and excess alcohol.
Work with your healthcare provider to determine if vitamin C supplements are appropriate as part of your treatment plan and to ensure your blood pressure is controlled.