Low-Dose Aspirin

Mechanisms of Action

Aspirin (acetylsalicylic acid) works through multiple pathways:

COX Inhibition:

• Irreversibly inhibits cyclooxygenase-1 (COX-1) and COX-2
• Reduces thromboxane A2 production → anti-platelet effect
• Reduces prostaglandin synthesis → anti-inflammatory

NF-κB Suppression:

• Inhibits nuclear factor kappa-B activation
• Suppresses downstream inflammatory genes (COX-2, iNOS, VCAM-1, ICAM-1)
• Blocks phosphorylation of IκBα

Antioxidant Effects:

• Reduces reactive oxygen species
• Inhibits nuclear translocation of thioredoxin
• May reduce oxidative damage associated with aging

Cancer Prevention Mechanisms:

• COX-2 inhibition reduces tumor-promoting prostaglandins
• Anti-platelet effect may reduce metastatic spread
• Direct effects on cell proliferation pathways
• Strongest evidence for colorectal cancer

The Weight Factor

A landmark 2018 Lancet analysis revealed that body weight significantly affects aspirin efficacy:

Higher doses (300-325mg) may be needed for heavier individuals, but this increases bleeding risk.

Age Considerations

The risk/benefit ratio shifts dramatically with age:

• Under 40: Generally not recommended (low baseline risk)
• 40-59: Consider if 10-year CVD risk ≥10%
• 60-69: Weaker recommendation, individual decision
• 70+: Generally NOT recommended to initiate (USPSTF 2022)

The ASPREE trial (19,114 adults 70+) found daily low-dose aspirin did not prolong healthy survival and was associated with increased bleeding and possibly higher cancer mortality.

Standard Protocol

Dose:

• 75-100mg daily (81mg "baby aspirin" in US)
• Take with food to reduce GI irritation
• Enteric-coated may reduce stomach upset (though absorption is slower)

Timing:

• Morning or evening, consistency matters more than timing
• Some evidence for evening dosing improving blood pressure effects

Who Should Consider:

• Adults 40-59 with elevated 10-year CVD risk (≥10%)
• Those with history of cardiovascular events (secondary prevention)
• Body weight under 70kg for low-dose efficacy
• Those with Lynch syndrome or high colorectal cancer risk

Who Should NOT Take:

• Adults 60+ without existing CVD (don't initiate)
• History of GI bleeding or ulcers
• Bleeding disorders
• Allergy to NSAIDs
• Taking anticoagulants (warfarin, etc.)
• Uncontrolled hypertension

Weight-Based Considerations

Duration

• Benefits accrue over years of use
• Stopping suddenly after long-term use may cause rebound cardiovascular events
• If stopping, discuss tapering with physician

Bleeding Risks

Gastrointestinal:

• Increased risk of stomach/intestinal bleeding
• Risk increases with age, alcohol use, H. pylori infection
• Symptoms: black/tarry stools, stomach pain, vomiting blood

Intracranial:

• Small increased risk of hemorrhagic stroke
• More concerning in those with uncontrolled hypertension

Risk Factors for Bleeding:

• Age 70+
• History of GI bleeding
• Concurrent NSAID use
• Anticoagulant use
• Heavy alcohol consumption
• H. pylori infection
• Uncontrolled hypertension

Other Side Effects

• Tinnitus (ringing in ears) - usually at higher doses
• Allergic reactions (rare but can be severe)
• Reye's syndrome in children with viral illness (do not give to children)

Drug Interactions

• Anticoagulants: Increased bleeding risk
• Other NSAIDs: May reduce aspirin's cardioprotective effect
• SSRIs: Increased GI bleeding risk
• Methotrexate: Increased toxicity
• ACE inhibitors: May reduce effectiveness

The ASPREE Warning

The ASPREE trial in adults 70+ found:

• No reduction in cardiovascular events
• Increased major bleeding
• Possible increase in cancer-related deaths
• No extension of disability-free survival

This led to updated guidelines recommending against initiating aspirin in this age group.

Ideal Candidates

• High CVD risk adults 40-59 with 10-year risk ≥10%
• Secondary prevention (history of heart attack/stroke)
• Lynch syndrome or high familial colorectal cancer risk
• Body weight under 70kg (for low-dose efficacy)
• No history of bleeding problems

May Benefit

• Adults 50-59 with moderate CVD risk factors
• Family history of colorectal cancer
• Those already tolerating aspirin well for years

Probably Should Avoid

• Adults 60+ without established CVD (don't start)
• Body weight over 80kg (low-dose may be ineffective)
• History of GI bleeding or ulcers
• Taking blood thinners
• Uncontrolled high blood pressure

Definitely Avoid

• Aspirin or NSAID allergy
• Active bleeding disorder
• Severe liver or kidney disease
• Children and teenagers (Reye's syndrome risk)
• Pregnancy (especially third trimester)

What to Monitor

Watch for Warning Signs:

• Black or tarry stools (GI bleeding)
• Unusual bruising
• Prolonged bleeding from cuts
• Blood in urine
• Severe headache (could indicate intracranial bleeding)

Regular Check-ups:

• Annual discussion with doctor about continuing
• Blood pressure monitoring
• Periodic CBC if on long-term therapy

Risk Assessment Tools:

• ASCVD Risk Calculator (for cardiovascular risk)
• HAS-BLED score (bleeding risk)

Signs to Stop and Seek Care:

• Vomiting blood or coffee-ground material
• Severe stomach pain
• Signs of allergic reaction
• Unexplained severe headache

Standard Options:

• Bayer Low-Dose Aspirin 81mg - Brand name, enteric-coated
• Kirkland Low-Dose Aspirin - Costco generic, good value
• CVS/Walgreens Generic 81mg - Store brands work identically

Notes:

• Generic aspirin is chemically identical to brand name
• Enteric coating may reduce stomach irritation
• No meaningful quality difference between brands
• This is one intervention where cheap generic is perfectly fine

Monthly Cost: $1-3/month

Cost-Benefit:

This is one of the cheapest interventions available. The limiting factor is not cost but whether you're an appropriate candidate based on age, weight, and risk factors.

Major Proponents:

• Rhonda Patrick, PhD - Covers aspirin research on FoundMyFitness

Aspirin is one of the most widely used medications in history, with over 100 years of clinical use. It remains on the WHO List of Essential Medicines and is used by millions for cardiovascular prevention worldwide.

Potentially Beneficial Combinations:

• Statin therapy: Complementary cardiovascular protection
• Blood pressure control: Reduces bleeding risk
• H. pylori treatment: Reduces GI bleeding risk if infected

Avoid Combining With:

• Other NSAIDs (ibuprofen may block aspirin's cardioprotective effect)
• Anticoagulants without medical supervision
• High-dose fish oil (additive bleeding risk)
• Alcohol (increases GI bleeding risk)