Dear Cherubs, a recent set of large observational studies has people whispering “wait, what?” — higher untreated cholesterol levels have been linked to lower cancer and overall mortality in several big cohorts. Before you cancel your doctor’s number, this is association, not revelation.

WHAT THE STUDY FOUND
A 2025 prospective analysis pooling UK Biobank and two Chinese cohorts reported that low or falling total cholesterol and LDL-C were associated with higher all-cause and cancer mortality, while higher cholesterol correlated mainly with heart-disease deaths. According to the UK Biobank summary, the analysis covered more than 480,000 participants (about 317,000 in UK Biobank plus ~163,000 in Chinese cohorts), with nearly a decade of follow-up and sensitivity checks to reduce obvious biases. A 2024 Scientific Reports study of nearly 60,000 newly diagnosed cancer patients similarly described a U-shaped relationship: both very low and very high cholesterol levels were linked to worse survival, with a middle zone showing the lowest risk. Those are real numbers, and real enough to merit attention — but they don’t automatically rewrite biology textbooks.

A lot of clever people have pointed out why this isn’t a tidy “cholesterol protects from cancer” headline. Observational data can’t prove cause. “Reverse causation” is a common culprit: early, undiagnosed cancer or other chronic illness can lower cholesterol (through weight loss, metabolic changes, or cachexia), making low cholesterol a marker of existing disease rather than a protective absence of villainy. Several cohort analyses and reviews — including work discussed in BMJ Open and other journals — have raised this exact possibility.

FASTING, AUTOPHAGY, AND WHY THIS ISN’T A CONTRADICTION
The other idea you mentioned — that fasting clears “toxic” cells — traces back to autophagy, the cellular self-cleaning mechanism for which Yoshinori Ohsumi won the 2016 Nobel Prize (autophagy helps cells recycle damaged proteins and organelles). Autophagy and cholesterol live on different scales: autophagy is a cellular stress response (fasting can activate it), while the cholesterol–mortality relationship is a population-level epidemiological observation. The two concepts can coexist. Fasting-induced autophagy might help remove damaged components in some situations, but that doesn’t mean circulating cholesterol levels are the thermostat for autophagy — nor that higher LDL is a public-health virtue.

So what should you do with this tea? Keep your context goggles on. These findings suggest cholesterol is more complicated than “bad equals bad,” and low cholesterol can sometimes flag frailty or hidden disease. They do not prove cholesterol itself protects against cancer, nor that people should avoid lipid-lowering therapy when clinically indicated. Randomized trials and mechanistic work are still the ticket for answers — and scientists are very busy buying those tickets.

In short: interesting, worth probing, and low-key inconvenient to simple narratives. We’ve been promised clear-cut villains before; science prefers messy plots.

Sources list — plain text, one per line:
UK Biobank — https://www.ukbiobank.ac.uk/publications/low-and-decreasing-cholesterol-levels-and-risk-of-all-cause-and-cause-specific-mortality-a-prospective-and-longitudinal-cohort-study/
Scientific Reports — https://www.nature.com/articles/s41598-023-50931-6
BMJ Open (Kip et al. 2024) — https://pmc.ncbi.nlm.nih.gov/articles/PMC10982736/
Nobel Prize (Yoshinori Ohsumi, autophagy) — https://www.nobelprize.org/prizes/medicine/2016/press-release/
Narrative review on fasting and cancer (reported) — https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9530862/
MDPI Cancers review on statins and cancer mortality — https://www.mdpi.com/2072-6694/14/12/2920
BMJ commentary on cholesterol and mortality (discussion of reverse causation) — https://www.bmj.com/content/371/bmj.m4266
Frontiers in Cardiovascular Medicine (L-shaped LDL-C in cancer survivors) — https://www.frontiersin.org/articles/10.3389/fcvm.2025.1593824/full
PMC review on reduced LDL in cachexia (reported) — https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7417624/
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