Daily aspirin amount needed to reduce cancer risk and cardiovascular events is dependent on your weight.

In March 2015, I posted an article about aspirin and melatonin being two easily accessible drugs that provided useful health benefits. In the case of aspirin, just 75 mg per day was shown to reduce cardiovascular events and the risk of cancer. More recent research - see below - shows that your weight dictates how much aspirin you should take each day to gain these health benefits. If you weigh under 70kg, 75mg of aspirin is sufficient. Over this weight, 325mg or more of aspirin needs to be taken each day to provide increased protection against cardiovascular events and cancer.

Effects of aspirin on risks of vascular events and cancer according to bodyweight and dose: analysis of individual patient data from randomised trials

Prof Peter M Rothwell, FMedSci

Prof Nancy R Cook, ScD

Prof J Michael Gaziano, MD

Prof Jacqueline F Price, PhD

Prof Jill F F Belch, MD

Maria Carla Roncaglioni, PhD

Takeshi Morimoto, MD

Ziyah Mehta, DPhil

Published: 12 July 2018

Summary

Background

A one-dose-fits-all approach to use of aspirin has yielded only modest benefits in long-term prevention of cardiovascular events, possibly due to underdosing in patients of large body size and excess dosing in patients of small body size, which might also affect other outcomes.

Methods

Using individual patient data, we analysed the modifying effects of bodyweight (10 kg bands) and height (10 cm bands) on the effects of low doses (≤100 mg) and higher doses (300–325 mg or ≥500 mg) of aspirin in randomised trials of aspirin in primary prevention of cardiovascular events. We stratified the findings by age, sex, and vascular risk factors, and validated them in trials of aspirin in secondary prevention of stroke. Additionally, we assessed whether any weight or height dependence was evident for the effect of aspirin on 20-year risk of colorectal cancer or any in-trial cancer.

Results

Among ten eligible trials of aspirin in primary prevention (including 117 279 participants), bodyweight varied four-fold and trial median weight ranged from 60·0 kg to 81·2 kg (p<0 75="" ability="" aspirin="" cardiovascular="" decreased="" events="" increasing="" mg="" of="" p="" reduce="" sub="" the="" to="" weight="" with="">interaction

=0·0072), with benefit seen in people weighing 50–69 kg (hazard ratio [HR] 0·75 [95% CI 0·65–0·85]) but not in those weighing 70 kg or more (0·95 [0·86–1·04]; 1·09 [0·93–1·29] for vascular death). Furthermore, the case fatality of a first cardiovascular event was increased by low-dose aspirin in people weighing 70 kg or more (odds ratio 1·33 [95% CI 1·08–1·64], p=0·0082). Higher doses of aspirin (≥325 mg) had the opposite interaction with bodyweight (difference p_interaction=0·0013), reducing cardiovascular events only at higher weight (p_interaction=0·017). Findings were similar in men and women, in people with diabetes, in trials of aspirin in secondary prevention, and in relation to height (p_interaction=0·0025 for cardiovascular events). Aspirin-mediated reductions in long-term risk of colorectal cancer were also weight dependent (p_interaction=0·038). Stratification by body size also revealed harms due to excess dosing: risk of sudden death was increased by aspirin in people at low weight for dose (p_interaction=0·0018) and risk of all-cause death was increased in people weighing less than 50 kg who were receiving 75–100 mg aspirin (HR 1·52 [95% CI 1·04–2·21], p=0·031). In participants aged 70 years or older, the 3-year risk of cancer was also increased by aspirin (1·20 [1·03–1·47], p=0·02), particularly in those weighing less than 70 kg (1·31 [1·07–1·61], p=0·009) and consequently in women (1·44 [1·11–1·87], p=0·0069).

Interpretation

Low doses of aspirin (75–100 mg) were only effective in preventing vascular events in patients weighing less than 70 kg, and had no benefit in the 80% of men and nearly 50% of all women weighing 70 kg or more. By contrast, higher doses of aspirin were only effective in patients weighing 70 kg or more. Given that aspirin's effects on other outcomes, including cancer, also showed interactions with body size, a one-dose-fits-all approach to aspirin is unlikely to be optimal, and a more tailored strategy is required.