What you carry at this position in your DNA and what research says about it.
Type 2 Diabetes Risk: 10/10 evidence, 93 publications.
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Sample genotype (not yours): C/C
Typical Diabetes Risk and Normal Blood Sugar
Typical blood sugar levels and a standard risk of metabolic conditions characterize this genotype.
What this genotype means: Typical fasting blood sugar levels; Standard risk of type 2 diabetes; Normal insulin secretion patterns.
Sample genotype (not yours): C/G
Moderately Increased Risk of Type 2 Diabetes
Slightly higher fasting blood sugar and a moderately increased risk of type 2 diabetes are associated with this genotype.
What this genotype means: Slightly elevated fasting blood sugar; Moderately increased risk of type 2 diabetes; Higher risk of gestational diabetes during pregnancy.
Sample genotype (not yours): G/G
Elevated Risk of Type 2 Diabetes
Higher fasting blood sugar and an increased risk of type 2 diabetes are associated with this genotype.
What this genotype means: Consistently higher fasting blood sugar; Increased risk of type 2 diabetes; Significantly higher risk of gestational diabetes.
Gene function and biological role
Gene Function: The MTNR1B gene encodes the melatonin receptor 1B, which is highly expressed in insulin-secreting beta cells of the pancreas [1]. Melatonin is a hormone primarily known for regulating sleep-wake cycles and circadian rhythms [2]. By binding to its receptors in the pancreas, melatonin helps coordinate the daily rhythms of insulin secretion [1]. Disruptions in this signaling pathway can impair the body's ability to manage blood sugar levels over time [2]. This makes the gene a critical link between sleep patterns, circadian biology, and metabolic health [1].
Variant Impact: The rs10830963 variant is an intron change in the MTNR1B gene that alters how the melatonin receptor is expressed in pancreatic cells [3]. Carrying the G allele increases the expression of these receptors, which paradoxically suppresses insulin release in response to glucose [4]. This reduction in insulin secretion leads to higher fasting blood sugar levels [5]. Over time, this mismatch in glucose regulation significantly raises the risk of developing metabolic conditions [6].
Key Insight: Melatonin, typically known as the sleep hormone, directly regulates insulin secretion in the pancreas, linking your sleep-wake cycle to blood sugar control.
Location: MTNR1B. Chromosome 11 · 11q14.3 · 93.0 Mb
Estimated prevalence by population
Global 60.5%; European 51.9%; African 86.8%; East Asian 32.1%; South Asian 34.4%; Americas 60.8%; Ashkenazi 58.6%; Finnish 41.8%; Middle Eastern 51.0%; Amish 28.2%.
Estimated CC genotype frequency.
Global 33.0%; European 40.3%; African 12.8%; East Asian 49.1%; South Asian 48.5%; Americas 34.4%; Ashkenazi 35.9%; Finnish 45.7%; Middle Eastern 40.8%; Amish 49.8%.
Estimated CG genotype frequency.
Global 6.5%; European 7.8%; African 0.5%; East Asian 18.8%; South Asian 17.1%; Americas 4.9%; Ashkenazi 5.5%; Finnish 12.5%; Middle Eastern 8.2%; Amish 22.0%.
Estimated GG genotype frequency.
Showing effects for C/C genotype
Cardiovascular & Metabolic
Diabetes & Glycemic Traits
Type 2 Diabetes. Evidence: 10/10. Source: PMID 22885922. Typical Risk.
Fasting Glucose. Evidence: 10/10. Source: PMID 19060907. Typical Levels.
Insulin Secretion. Evidence: 7/10. Source: PMID 25524916. Typical Secretion.
HbA1c. Evidence: 10/10. Source: PMID 28898252. Typical Levels.
Endocrine & Reproductive
Pregnancy & Birth Complications
Gestational Diabetes. Evidence: 10/10. Source: PMID 35220425. Typical Risk.
Offspring Birth Weight. Evidence: 8/10. Source: PMID 27680694. Typical Weight.
Showing effects for C/G genotype
Type 2 Diabetes. Evidence: 10/10. Source: PMID 22885922. ~1.1x Higher Risk.
Fasting Glucose. Evidence: 10/10. Source: PMID 19060907. Slightly Elevated.
Insulin Secretion. Evidence: 7/10. Source: PMID 25524916. Slightly Reduced.
HbA1c. Evidence: 10/10. Source: PMID 28898252. Slightly Higher.
Gestational Diabetes. Evidence: 10/10. Source: PMID 35220425. ~1.4x Higher Risk.
Offspring Birth Weight. Evidence: 8/10. Source: PMID 27680694. Slightly Higher.
Showing effects for G/G genotype
Type 2 Diabetes. Evidence: 10/10. Source: PMID 22885922. ~1.2x Higher Risk.
Fasting Glucose. Evidence: 10/10. Source: PMID 19060907. Elevated.
Insulin Secretion. Evidence: 7/10. Source: PMID 25524916. Reduced Secretion.
HbA1c. Evidence: 10/10. Source: PMID 28898252. Higher Levels.
Offspring Birth Weight. Evidence: 8/10. Source: PMID 27680694. Higher Weight.
What this genotype means for the people who carry it
Sample genotype: CC (Homozygous)
Two copies of the C allele represent the baseline genetic profile for blood sugar regulation at this locus. Pancreatic beta cells maintain typical melatonin receptor levels, allowing for normal insulin release when blood sugar rises [1]. Consequently, fasting glucose levels and long-term HbA1c measurements remain within the typical range [2] [3]. The risk of developing type 2 diabetes or gestational diabetes during pregnancy is not elevated [4] [5]. Maintaining a balanced diet and regular exercise continues to support healthy metabolic function.
Typical fasting blood sugar levels; Standard risk of type 2 diabetes; Normal insulin secretion patterns.
Sample genotype: CG (Heterozygous)
One copy of the G allele alters melatonin receptor activity in the pancreas, which can mildly suppress insulin secretion [1]. This reduction in insulin release often leads to slightly elevated fasting blood sugar levels [2]. Long-term markers of glucose control, such as HbA1c, may also be slightly higher than average [3]. During pregnancy, this genetic variation increases the likelihood of developing gestational diabetes [4]. Managing carbohydrate intake and staying physically active are highly effective ways to offset this genetic predisposition.
Slightly elevated fasting blood sugar; Moderately increased risk of type 2 diabetes; Higher risk of gestational diabetes during pregnancy.
Sample genotype: GG (Homozygous)
Pancreatic beta cells with two G alleles express more melatonin receptors, which significantly dampens insulin secretion [1]. This blunted insulin response results in consistently higher fasting blood glucose levels [2]. Long-term blood sugar markers like HbA1c are typically elevated compared to those with other genotypes [3]. Pregnant individuals with this genotype face a notably higher risk of developing gestational diabetes [4].
Consistently higher fasting blood sugar; Increased risk of type 2 diabetes; Significantly higher risk of gestational diabetes.
Variants with shared genetic architecture
rs1387153 · MTNR1B Gene · Chr 11 · Blood Sugar Regulation
rs10830962 · MTNR1B Gene · Chr 11 · Gestational Diabetes Risk
rs4753426 · MTNR1B Gene · Chr 11 · Diabetes Risk
A central role for GRB10 in regulation of islet function in man.
Melatonin and the pathologies of weakened or dysregulated circadian oscillators.
Variants in MTNR1B influence fasting glucose levels.
Content updated August 2026.
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