There is a common belief that eating onions can thin your blood. The thought is that onions contain certain compounds that can act as natural blood thinners and reduce the risk of clotting. But is there any truth to this idea? Do onions really have blood thinning properties? Let’s take a closer look at the evidence.
What Gives Onions Their Strong Flavor?
The distinctive, pungent taste and smell of onions come from sulfur-containing compounds. Onions contain two main categories of these sulfur compounds:
– Amino acid sulfoxides – mainly isoalliin
– Thiosulfinates – mainly allyl methyl trisulfide
When an onion is cut or crushed, the damage to the cells releases an enzyme called alliinase. This enzyme breaks down the amino acid sulfoxides into various sulfenic acids and thiosulfinates (1).
These volatile sulfur compounds give onions their intense flavor and are responsible for bringing tears to your eyes when you cut an onion. They also provide many of the potential health benefits.
Do Onions Have Natural Blood Thinning Properties?
Some sources claim that onions have natural blood thinning effects. This stems from their sulfur-containing compounds, which may have anticoagulant or antiplatelet properties.
Anticoagulants prevent blood clotting, while antiplatelet compounds prevent platelets in the blood from sticking together and forming clots. By inhibiting clot formation, these substances help blood flow smoothly and reduce the risk of dangerous clots.
There is some research to support that certain compounds in onions may influence platelet function and provide antithrombotic effects:
– Ajoene – This compound formed from allicin in garlic may also be present in small amounts in onions. Studies show it can inhibit platelet aggregation (2).
– Quercetin – This antioxidant flavonoid found in onions may prevent platelet clumping by inhibiting thromboxane formation (3).
– Adenosine – Onions contain adenosine and other sulfur compounds that exhibit antiplatelet activity and may prevent platelet aggregation (4).
However, the concentrations of these compounds in onions are fairly low compared to therapeutic doses used in blood thinning medication. More research is needed to determine if eating onions provides enough of these compounds to significantly thin the blood or reduce clotting.
Evidence on Onions and Clotting
Some small studies have looked directly at the effects of onions on markers of clotting function in humans:
– A study in 12 healthy men found eating 100 g of raw onions per day for 1 week reduced platelet aggregation compared to a control diet (5).
– One small study in rats showed onion juice inhibited platelet aggregation when given via IV, but not when fed orally (6).
– Another study in human subjects showed no effect on platelet function when 15 volunteers ate 60-100 g of raw onions per day for a week (7).
The evidence remains inconsistent on whether eating normal amounts of onions can impact platelet activity enough to thin the blood. Larger scale studies are still needed.
Other Possible Blood Thinning Effects
In addition to their potential antiplatelet properties, some sources suggest onions may thin the blood by:
– Improving circulation and blood flow
– Lowering blood pressure
– Lowering cholesterol
Onions are a good source of flavonoids, which can help improve circulation by strengthening blood vessels and preventing plaque buildup. Onions also contain compounds that may help relax blood vessels and reduce blood pressure.
Lowering blood pressure reduces the risk of blood clots. Onions’ potential cholesterol-lowering effects could also improve blood flow. But more studies are needed on these mechanisms.
Risks of Onion Blood Thinning Effects
While onion’s blood thinning potential seems promising, there are some risks to consider:
– Could increase bleeding risk – Like aspirin and other blood thinners, onions might prolong bleeding time. This could be harmful for those with clotting disorders or taking blood thinning medication.
– Lack of evidence on appropriate doses – It’s unclear how many onions need to be consumed to achieve therapeutic blood thinning effects, if any. Eating too many onions could potentially thin the blood too much.
– Drug interactions – Onions may enhance the effects of actual blood thinning medications like warfarin and increase bleeding risk. More research is needed.
– Gastrointestinal irritation – Eating large amounts of raw onions can irritate the GI tract. This could counteract any heart-protective effects.
More studies are needed to determine safe and effective dosing before onions can be recommended as blood thinners. Speak to your doctor before increasing onion intake, especially if taking other blood thinning medication.
Safer Ways Onions May Protect Heart Health
Though onions may not be potent enough blood thinners to rely on, studies show they can support heart health in other ways:
– Lowering blood pressure – Onions are rich in quercetin, sulfur compounds, and polysaccharides that help relax blood vessels and reduce hypertension (8).
– Reducing cholesterol – Animal and human studies show onion consumption lowers harmful LDL cholesterol while boosting HDL (9, 10).
– Controlling blood sugar – Onions contain compounds that help regulate blood sugar, which protects artery health and reduces heart disease risk (11).
– Providing antioxidants – Onions are high in polyphenols and flavonoids that counter inflammation and protect against atherosclerosis (12).
– Supporting healthy weight – Onions are low in calories and high in fiber and water content, which helps reduce obesity and associated heart risks (13).
So while onions likely do not contain enough medicinal compounds to seriously impact clotting, their wealth of antioxidants, anti-inflammatories, and micronutrients still make them a heart-healthy choice.
Who May Benefit From Onion’s Mild Blood Thinning Effects
While more research is needed, onions may provide some mild anticoagulant activity:
– People at increased heart attack/stroke risk – For those with hypertension, diabetes, obesity, or atherosclerosis, onions may provide a small degree of platelet inhibiting effects.
– Individuals prone to clots – Those immobile for long periods or who have a genetic clotting disorder like Factor V Leiden may also get a minor protective benefit.
– As an addition to other blood thinners – Under medical supervision, onion intake may boost the effectiveness of lower dose blood thinning medication.
However, onions’ anticoagulant effects are not strong enough to replace medication. Anyone already taking blood thinners should not dramatically increase their onion intake without speaking to their doctor due to bleeding risks.
Key Takeaways on Onions and Blood Thinning
Some key points to keep in mind on the blood thinning effects of onions:
– Onions contain certain sulfur compounds and flavonoids that may have mild antiplatelet and anticoagulant properties.
– Evidence is inconsistent on whether eating normal amounts of onions significantly affects clotting function in humans.
– More studies are needed to establish effective doses and safety. Eating excessive onions could dangerously thin the blood.
– Onions may provide additive effects and increase bleeding risk when combined with blood thinning medication.
– While onions likely do not thin the blood enough to rely on therapeutically, they offer other benefits to heart health like lowering cholesterol and blood pressure.
– Those at higher cardiac risk may get a modest protective benefit from onions’ potential antiplatelet effects.
Overall, more clinical trials are required to truly determine if onions thin the blood sufficiently to reduce heart attack and stroke risk. But onions can still be part of a heart-healthy eating pattern due to their nutrition and antioxidant content.
How Can You Incorporate More Onions Into Your Diet?
Here are some simple ways to add more onions to your meals and potentially harness their cardiovascular benefits:
– Make French onion or onion bhaji soup. Onion soups allow you to pack in several onions at once.
– Top sandwiches, burgers, pizza, and flatbreads with sliced raw onions.
– Add diced or thinly sliced onions to omelets, scrambled eggs, and sautéed veggie dishes.
– Roast onions whole, sliced, or chopped alongside other veggies at 400°F until caramelized.
– Grill sliced red onions as part of foil packet meals along with zucchini, squash, and other produce.
– Add onion powder or flakes to dressings, dips, and sauces for an onion boost without the texture.
– Pickle red onions in vinegar. Use them to garnish salads, tacos, grain bowls, and more.
– Make quick-pickled raw onion rings to use as burger topping or salad add-ins.
Should You Avoid Onions If Taking Blood Thinners?
If you are already on prescription blood thinning medication, suddenly increasing your onion intake could potentially cause adverse effects. Some tips include:
– Talk to your doctor before adding more onions to your diet. Get their advice on safe amounts.
– Monitor for signs of bleeding like easy bruising, frequent nosebleeds, bleeding gums, heavy periods, and bloody stools.
– Watch your intake of other foods/herbs with blood thinning effects like garlic, ginger, ginkgo, and turmeric.
– Avoid combining high-onion foods with blood thinning medications at the same meal.
– Stick to cooked onions rather than large amounts of raw onions, which are more potent.
– Have your INR checked regularly if taking warfarin to ensure your dose is still appropriate.
Blood thinners and onion interactions are not well studied, so it’s smart to exercise some caution and check with your doctor first if increasing onion intake substantially.
The Bottom Line
Though they may provide some mild antiplatelet, anticoagulant activity, onions are unlikely to thin the blood significantly enough to replace medical blood thinners. But incorporating more onions into your diet through soups, salads, main dishes, and more can still benefit heart health thanks to their combination of antioxidants, sulfur compounds, and nutrients.
Onions, like garlic and other allium vegetables, do appear to have therapeutic potential. But more clinical studies are needed to understand proper dosing and medical applications. For now, boosting onion intake in culinary ways can provide protective compounds without over-thinning the blood.
As always, people taking blood thinning medication should exercise caution with onions and other foods that may interfere with clotting. Start by checking with your doctor and monitoring for unusual bleeding or bruising when ramping up onion intake.
