Most people get a blood test and walk away caring about two numbers: cholesterol and blood sugar. If both look acceptable, they assume all is well. But acceptable is not the same as optimal — and when it comes to brain health, the gap between those two words can span decades of silent damage.
There is a set of tests that most doctors do not routinely order, and a set of numbers within the tests they do order that most doctors do not adequately explain. Understanding both could be among the most important things you do for your long-term cognitive health.
The Tests That Actually Matter for Your Brain
Fasting Insulin
If you get only one test from this list, make it this one. Long before blood sugar begins to climb as someone becomes diabetic, fasting insulin levels rise — signalling that the pancreas is working overtime to compensate for excess dietary carbohydrates. It is an early warning system that can get you ahead of the diabetes curve by years, sometimes decades. Since insulin resistance is now closely linked to brain disease, this single number carries enormous predictive power.
Fasting Blood Glucose
This is the standard diabetes screening test — a measure of blood sugar after at least eight hours without food. A result between 70 and 100 mg/dL is considered normal. Do not be reassured too quickly. A blood sugar pushing 100 is not as benign as that range implies. At that level, insulin resistance is already underway and the risk for brain disease is elevated. A more protective target is below 95 mg/dL.
Hemoglobin A1C
Unlike a single fasting glucose reading, the A1C test reveals an average blood sugar level over the preceding ninety days. It measures glycation — the process by which sugar bonds to protein, in this case the protein haemoglobin. Glycated haemoglobin is one of the strongest predictors of both Alzheimer’s disease risk and brain shrinkage. An A1C between 4.8 and 5.4 percent is considered optimal.
Fructosamine
Similar to A1C but covering a shorter window of two to three weeks, the fructosamine test offers a more immediate picture of blood sugar control. Target levels fall between 188 and 223 mol/L. Its shorter timeframe means it can also show the effects of dietary changes more quickly — positive results can become visible within weeks.
C-Reactive Protein (CRP)
CRP is a marker of systemic inflammation. Ideal levels fall below 1.0 mg/L, with anything up to 3.0 mg/L considered acceptable. Chronic low-grade inflammation is now understood to be a driver of neurological disease, and this test provides a direct measure of how inflamed your body currently is.
Homocysteine
Homocysteine is an amino acid produced naturally by the body, but elevated levels are associated with atherosclerosis, heart disease, stroke, and dementia. A level above 10 mol/L is considered elevated — and research published in the New England Journal of Medicine found that a level of just 14 was associated with a doubling of Alzheimer’s risk.
There is another dimension to homocysteine worth noting: high levels have been shown to triple the rate of telomere shortening. Telomeres are the protective caps on the ends of chromosomes that serve as a biological indicator of how quickly you are ageing. The faster they shorten, the faster the clock runs. The good news is that homocysteine levels are among the most responsive to intervention and can often be improved relatively quickly.
Glyphosate Urine Test
Glyphosate is the active ingredient in the widely used weed killer Roundup, applied extensively in conventional agriculture. A urine test can now detect the presence of this chemical in the body. The target is straightforward: undetectable levels, measured as ug/L.
Vitamin D
Vitamin D is technically not a vitamin at all — it is a hormone, produced in the skin upon exposure to ultraviolet light. By definition, vitamins cannot be produced by the body. Vitamin D can, which places it in a different category entirely.
Its effects on the brain are extensive. Researchers have identified approximately 3,000 binding sites on the human genome for vitamin D. It helps regulate enzymes in the brain and cerebrospinal fluid involved in producing neurotransmitters, stimulating nerve growth, and protecting neurons from free radical damage. Higher vitamin D levels are also associated with longer telomeres — a biological marker of slower ageing.
Normal range is 30 to 100 ng/mL, but optimal brain health is associated with levels around 80 ng/mL. The majority of people are deficient, largely due to indoor lifestyles and routine use of sunscreen. Those living at northern latitudes are at particular risk.
When the Body Switches Fuel
Under normal conditions, the brain runs on glucose. Between meals, the liver and muscles release stored glycogen to maintain a steady supply. But glycogen stores are limited. Once depleted, the body begins producing glucose from amino acids — primarily drawn from muscle protein. You get fuel, but at the cost of muscle breakdown.
There is a better alternative. When glucose is scarce and fat metabolism takes over, the liver produces ketones — specialized molecules that serve as a highly efficient fuel source for the brain. One in particular, beta-hydroxybutyrate (beta-HBA), plays a central role. It allows the brain to function well during periods of food scarcity, reduces dependence on muscle-derived glucose, and helps preserve lean mass.
Fasting is one of the most effective ways to shift the body into this metabolic state. Rather than breaking down muscle to sustain the brain, the body draws on fat stores instead — a more sustainable and less destructive energy source.
Turmeric: The Spice With a Neurological Profile
Turmeric, the yellow-pigmented spice central to curry powder, has been used in Chinese and Indian medicine for thousands of years. Modern research is beginning to catch up with what traditional medicine long understood.
Curcumin — the most active compound in turmeric — activates genes that produce antioxidants protecting the mitochondria. It reduces cellular inflammation, improves glucose metabolism, and supports a healthy gut microbiome. Studies have shown it can enhance the growth of new brain cells, increase DHA levels in the brain, and in some individuals produce antidepressant effects comparable to pharmaceutical interventions.
For those not regularly eating curry, a supplement of 500 mg twice daily provides a practical alternative.
The Gut-Brain Axis: Prebiotics and the Damage of Antibiotics
The bacteria living in your gut are not passive residents. They actively influence inflammation, neurotransmitter production, immune function, and brain health. Feeding them well is not optional.
Prebiotics are the compounds that gut bacteria consume to fuel their growth. To qualify, a substance must be non-digestible — passing through the stomach intact — capable of being fermented by intestinal bacteria, and genuinely beneficial in its effects. Prebiotic dietary fibre meets all three criteria, and its influence on the gut microbiome is now linked to anti-cancer, anti-diabetic, anti-dementia, and weight-regulating effects.
Antibiotics are the opposite force. They are, by their nature, anti-life — designed to kill bacteria, which means they kill beneficial bacteria alongside harmful ones. A single course of antibiotics can alter the composition of the gut microbiome for months, and new research suggests the effects may persist for the rest of a person’s life. This does not mean antibiotics should be avoided when genuinely necessary. It means their use should be deliberate, and that restoring gut balance afterward is not optional — it is part of the treatment.
The Bigger Picture
Brain disease does not announce itself suddenly. It builds over years and decades, driven by insulin resistance, inflammation, nutritional deficiencies, and accumulated chemical exposure — most of which are measurable, most of which are modifiable, and almost none of which are captured by a standard annual blood panel.
The tests exist. The knowledge exists. What remains is the decision to ask for them — and to take the numbers seriously before they become symptoms.
Source : Power Up Your Brain: The Neuroscience of Enlightenment by David Perlmutter, Alberto Villoldo
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