The Cholesterol
Road.

Remove it, and you remove far more than a number.

This is the sister road to insulin and the amino-acid pathways of the series. Where those describe what the body builds from protein, this one runs from a single fat molecule — cholesterol — to the entire steroid hormone family. Lower it and you don't simply move a figure on a lipid panel: you touch the raw material of the stress response, the salt-and-pressure system, fertility, bone and immune regulation, and fat digestion itself.

Mostly, you make it. Roughly three-quarters of the cholesterol in your blood is built inside your body — chiefly the liver — and only the minority comes from food. When you eat more, the body makes less to compensate.[2] It's a regulated internal factory, not a passive tank filled by the plate — which is why, for most people, dietary cholesterol moves blood cholesterol only modestly.

The gateway every steroid passes through.

Even if it never became a single hormone, cholesterol would be indispensable: it's a structural part of every cell membrane, especially concentrated in the myelin that insulates your nerves — the brain is one of the most cholesterol-rich organs you have — and it's the raw material of bile, without which fat and the fat-soluble vitamins can't be absorbed.

But here is the road proper. Every steroid hormone begins with one conversion: cholesterol to pregnenolone. It happens inside the mitochondria, in two moves — a transport protein (StAR) ferries cholesterol in, and an enzyme (CYP11A1) makes the cut.[1] Pregnenolone is the master precursor — the mother of every steroid that follows. From here, the road forks.

Cortisol raises blood sugar — from both ends.

Cortisol is the sustained-stress hormone, and its central metabolic job is to raise blood glucose. It does it from both ends of the ledger at once — turning the supply of glucose up, and turning the disposal of glucose down. That second half is where it opposes insulin: it deliberately makes muscle and fat more insulin-resistant.[5]

• Supply up: it drives the liver to manufacture new glucose, and breaks down muscle and fat to supply the raw material for it.
• Disposal down: it blunts insulin's signal in muscle and fat, so fewer glucose doors open — and frees fatty acids that themselves worsen insulin resistance.

In an acute threat this is elegant: cortisol rations glucose to the brain (which takes it up without insulin) while muscle burns fat. The trouble is the word chronic. Run that programme continuously — unremitting stress, wrecked sleep, or the extreme of Cushing's — and you get sustained high glucose, driven insulin resistance, and fat pushed to the visceral belly depot.

Salt, pressure — and the sex hormones.

Aldosterone, the salt branch, tells the kidneys to hold sodium; water follows, and pressure rises. It's the hormone behind the blood-pressure chapter's salt rope — and insulin pulls on the very same rope, promoting sodium retention itself.[9] Two chapters, the same system from two ends.

The sex-hormone branches are wired to metabolism more tightly than most people realise. Two links matter:

• Fat is an oestrogen-making organ. Adipose tissue carries the enzyme aromatase and actively converts androgens into oestrogens — so body composition shifts the hormonal balance in both sexes.[8]
• Insulin frees the sex hormones. Most sex hormone travels bound to a carrier, SHBG, made by the liver — and insulin suppresses it.[6] Higher insulin means lower SHBG, so more free, active hormone. In PCOS — since 2026 officially renamed PMOS — high insulin drives ovarian androgens and lowers SHBG at once[7] — the reproductive symptoms with a metabolic root.

A vitamin that's really a hormone — and the body's biggest cholesterol exit.

Vitamin D is misnamed. It's not a vitamin you must eat but a hormone your body makes, from cholesterol, using sunlight — its precursor sits one step from cholesterol in your skin, UVB turns it into vitamin D, and the liver and kidney finish it.[3] Chemically it's a secosteroid, and it acts like a hormone, governing calcium and immune function. It's where this road meets the sunlight thread of the series: the same UVB that drives the skin's melanin cascade also builds vitamin D, in the very same tissue, from a cholesterol derivative. One thing worth stating plainly, because it's widely muddled — vitamin D needs the stronger UVB of the higher, middle-of-the-day sun. A rough rule: if your shadow is longer than you are tall, little is being made. The low, slanting light of early morning carries almost no UVB — and at our latitude there's a long stretch of winter when even midday sun makes none at all, which is exactly why vitamin D is so often the one thing that has to come from food or a supplement.

Bile acids are cholesterol's largest exit — its main disposal route, and the reason you can absorb fat at all. Long dismissed as mere detergents, they're now known to be signalling molecules, acting through the FXR and TGR5 receptors to influence how the body handles glucose and fat, in a two-way conversation with the gut microbiome.[4] Most of the cholesterol you make is doing the daily work of digestion and signalling through this exit — not being "used up" by hormones at all.

Most of this road isn't something to "boost."

The body regulates cholesterol and steroid production tightly. The useful moves are mostly about not disrupting the system and supporting the state it runs best in — not forcing more hormone out of it.

• Don't fear dietary cholesterol — but don't over-rely on it. For most people it moves blood cholesterol modestly and isn't the limiting factor for hormones. Eat whole foods that contain it without dread, and without the belief they'll "raise your hormones."
• Statins are a doctor's conversation, never a solo decision. If you want to understand a statin's reach into this pathway — including CoQ10 and any symptoms — that's a good discussion with your prescriber. Never change the dose on your own.
• Sunlight supports the vitamin-D arm — though vitamin D specifically needs the stronger midday sun, not low morning light, and comes up short at our latitude through winter — and sun exposure doubles up with benefits elsewhere in the series.
• Blood sugar and body composition are the strongest lever, because insulin is wired into the sex-hormone and aldosterone branches. Lowering an elevated insulin load reaches more of this road than any supplement.
• Be sceptical of precursor and hormone supplements. DHEA, pregnenolone and the like are real steroids with real risks, not gentle nutrients. A genuine deficiency is diagnosed and treated with a doctor — not guessed at from a shelf.

The same shape as its sister road.

One precursor, a branching tree of products, a short cast of enzymes running on the same mineral tools — and threaded through nearly every branch, insulin, quietly setting the terms. It's the identical architecture to the amino-acid roads: a single starting molecule opening into a whole family of essential things.

Which is the quiet correction at the heart of it. The molecule medicine taught us to lower at all costs is the one the entire steroid system is built from. That doesn't mean high cholesterol never needs treating — it can, and sometimes should. It means the story we were told was half a story, and the missing half is the one that makes the biology make sense.

One molecule. A whole endocrine system. Worth understanding before it is feared.