Fasting glucose / type 2 diabetes (MTNR1B)

MTNR1B is a melatonin receptor on the insulin-producing cells of the pancreas. A common variant raises fasting blood sugar slightly and modestly increases type 2 diabetes risk, partly by tying melatonin and sleep timing to insulin release.

What this MTNR1B variant does

MTNR1B encodes one of the two melatonin receptors, and it is expressed on the insulin-producing beta cells of the pancreas. Melatonin rises at night and suppresses insulin secretion, which makes sense for a body that is not eating. The risk version of this variant increases receptor expression in beta cells, strengthening that suppression.

The practical consequence is a slightly higher fasting glucose and a weaker early insulin response to glucose, and a genuine link between this variant and the timing of meals relative to melatonin.

How strong the evidence is

The association is one of the most robust in glycaemic genetics. In this site's evidence file the catalogued type 2 diabetes association comes from a study of more than 2.5 million people with a p-value below 1e-130, supported by 25 publications.

The effect on fasting glucose has been measured at around 0.21 mmol/L per risk allele, and the variant is also one of the strongest known genetic contributors to gestational diabetes, with reported odds ratios in the range of about 1.5 to 1.8 depending on diagnostic criteria.

The circadian angle, stated carefully

Because the mechanism runs through melatonin, this is one of the few common variants with a plausible timing dimension: eating late, when melatonin is high, is a different metabolic situation for a carrier than for a non-carrier, and studies of meal timing and this genotype have reported interactions.

That literature is still developing and the effects reported are small. It is enough to make the mechanism interesting, not enough to justify prescribing yourself a meal schedule from a genotype.

How common it is

This is a common variant everywhere and especially in East Asia: in 1000 Genomes reference data about 19% of East Asian-ancestry individuals carry two risk copies and 48% carry one, against roughly 8% and 40% in European-ancestry samples, and it is less common in African-ancestry samples.

What this variant does not tell you

A shift of about 0.2 mmol/L in fasting glucose is small relative to the range that separates normal from diabetes, and a single variant does not determine either. Only a blood test does.

For anyone pregnant or planning pregnancy, the gestational diabetes association is the part of this with real-world weight, and screening for gestational diabetes is routine in pregnancy care regardless of genotype.

What each rs10830963 genotype means

rs10830963 has three possible genotypes: CC, CG and GG.

Typical fasting glucose (MTNR1B) (rs10830963 CC). You don't carry the MTNR1B blood-sugar variant, so as far as this gene goes, your fasting glucose and type 2 diabetes risk sit at the baseline. Weight, diet and activity still matter most.

Slightly higher fasting glucose (rs10830963 CG). You carry one copy of the MTNR1B variant linked to slightly higher fasting blood sugar and a modest increase in type 2 diabetes risk. The effect is small and very manageable with the usual diet, activity and weight habits.

Higher fasting glucose (rs10830963 GG). You have two copies of the MTNR1B variant tied to higher fasting blood sugar and a modestly raised type 2 diabetes risk. It's a tendency, not a diagnosis: lifestyle is the main lever, and a simple fasting-glucose or HbA1c blood test shows your actual level.

Evidence & sources

This variant appears in 25 published genetic studies: PubMed 22885922 · PubMed 24509480 · PubMed 28254843 · PubMed 28869590 · PubMed 29743933 · PubMed 30054458 · PubMed 30297969 · PubMed 30595370 · PubMed 31021400 · PubMed 32499647 · PubMed 32541925 · PubMed 33402679 · PubMed 34059833 · PubMed 34610981 · PubMed 34951656 · PubMed 35551307 · PubMed 35902682 · PubMed 36329257 · PubMed 36738649 · PubMed 38116116 · PubMed 38374256 · PubMed 38685053 · PubMed 39024449 · PubMed 39379762 · PubMed 40210677.

Common questions

Should I avoid eating late because of this variant? The mechanism gives that idea a real basis, since the variant strengthens melatonin's suppression of insulin and melatonin is high at night. The measured effects are small, though, and there is no evidence that acting on a genotype specifically improves outcomes. Regular meal timing is reasonable advice for most people either way.

Does this variant cause gestational diabetes? It is one of the stronger genetic contributors, with odds ratios reported around 1.5 to 1.8, which still leaves most carriers unaffected and most cases occurring in people without it. Screening in pregnancy is routine and is what actually detects it.

Related

Age-related macular degeneration risk · Alzheimer's disease · APOE type (Alzheimer's & cholesterol) · Atrial fibrillation · Autoimmune protection (IL23R R381Q) · Factor V Leiden thrombophilia · Rheumatoid arthritis