Associations between urinary heavy metal concentrations and blood pressure in residents of Asian countries.

BACKGROUND: Previous studies have suggested that exposures to heavy metals (arsenic, cadmium, lead, and selenium) may be associated with differences in blood pressure. However, the findings of these studies have been inconsistent. This study was performed to examine the associations between urinary heavy metal concentrations and blood pressure among residents of four Asian countries (Bangladesh, Indonesia, Nepal, and Vietnam). METHODS: This cross-sectional study examined 1899 adults in four Asian countries. Urinary concentrations of heavy metals were measured by inductively coupled plasma mass spectrometry. A questionnaire survey was administered regarding individual characteristics. Anthropometric measurements (height and weight) were performed. Systolic and diastolic blood pressures were measured after a short rest. Multiple linear regression models were applied to investigate associations between urinary heavy metal concentrations and blood pressure after adjustments for age, sex, and body mass index. RESULTS: The geometric means of the urinary concentrations of arsenic, cadmium, lead, and selenium were 84.6, 0.885, 2.09, and 16.5 µg/g creatinine, respectively. The urinary arsenic concentrations were slightly higher than those typically reported in non-polluted populations, while urinary cadmium, lead, and selenium concentrations were equivalent or slightly lower. The urinary lead concentrations were positively associated with both systolic and diastolic blood pressure, but urinary selenium concentrations were negatively associated with them. CONCLUSIONS: Variations in the urinary concentrations of lead and selenium were associated with blood pressure at low levels of exposure/intake.

Admixture with indigenous people helps local adaptation: admixture-enabled selection in Polynesians.

BACKGROUND: Homo sapiens have experienced admixture many times in the last few thousand years. To examine how admixture affects local adaptation, we investigated genomes of modern Polynesians, who are shaped through admixture between Austronesian-speaking people from Southeast Asia (Asian-related ancestors) and indigenous people in Near Oceania (Papuan-related ancestors). METHODS: In this study local ancestry was estimated across the genome in Polynesians (23 Tongan subjects) to find the candidate regions of admixture-enabled selection contributed by Papuan-related ancestors. RESULTS: The mean proportion of Papuan-related ancestry across the Polynesian genome was estimated as 24.6% (SD = 8.63%), and two genomic regions, the extended major histocompatibility complex (xMHC) region on chromosome 6 and the ATP-binding cassette transporter sub-family C member 11 (ABCC11) gene on chromosome 16, showed proportions of Papuan-related ancestry more than 5 SD greater than the mean (> 67.8%). The coalescent simulation under the assumption of selective neutrality suggested that such signals of Papuan-related ancestry enrichment were caused by positive selection after admixture (false discovery rate = 0.045). The ABCC11 harbors a nonsynonymous SNP, rs17822931, which affects apocrine secretory cell function. The approximate Bayesian computation indicated that, in Polynesian ancestors, a strong positive selection (s = 0.0217) acted on the ancestral allele of rs17822931 derived from Papuan-related ancestors. CONCLUSIONS: Our results suggest that admixture with Papuan-related ancestors contributed to the rapid local adaptation of Polynesian ancestors. Considering frequent admixture events in human evolution history, the acceleration of local adaptation through admixture should be a common event in humans.

Association study of CREBRF missense variant (rs373863828:G > A; p.Arg457Gln) with levels of serum lipid profile in the Pacific populations.

BACKGROUND: A missense variant (rs373863828:G > A; p.Arg457Gln) of the CREBRF gene is strongly associated with a higher body mass index (BMI; kg/m2) in Polynesian populations. This variant has also been reported to be associated with lower total cholesterol in Samoans. AIM: The aim of this study is to examine the association of rs373863828:G > A with levels of serum lipids in four Pacific populations. METHODS: A total of 613 adult subjects were recruited from Tonga (Polynesians) and the Solomon Islands (Melanesians and Micronesians). Multiple regression analyses adjusted for age and sex were performed to examine the association of rs373863828 with levels of serum lipids in each population. RESULTS: A significant association of rs373863828:G > A with lower level of HDL-cholesterol was detected in the Tonga population (ß = -3.32 and p-value = 0.030). The expected change in HDL-cholesterol with respect to a single copy of the rs373863828-A allele was 3.32 mg/dL. However, the association between rs373863828-A and lower levels of HDL-cholesterol was not significant after further adjustment for BMI in the Tonga population (ß = -2.32 and p-value = 0.13). CONCLUSIONS: The rs373863828-A allele may not directly affect the level of serum HDL-cholesterol independent of BMI. To confirm the present findings, association studies with large sample sizes and functional analyses are required.

Dietary patterns and serum of DDT concentrations among reproductive-aged group of women in Bangladesh.

This research was conducted in order to propose ways to reduce human exposure to DDT, especially for women of reproductive age in Bangladesh, and to find a relation between DDT exposure levels in serum and questionnaire information including sociodemographic and food frequency (FFQ). In this study, a significant relationship was found between the education level and BMI, and the serum p,p'-DDE concentration. This result suggests that people with higher education (relating to higher income) and BMI in Bangladesh actively buy expensive foodstuff, like meat and/or fatty fish, which relates to a higher fat intake. Additionally, a weak positive relationship between p,p'-DDE concentration in serum and the frequency of beef consumption was observed among the nullipara women subgroup. In a previous study, beef and fish showed large contributions on DDT intake of Bangladesh population. Those results suggest that the control of fatty food consumption such as meat (beef) and marine fish might help to regulate the levels of DDT.

Intake of DDT and its metabolites through food items among reproductive age women in Bangladesh.

This study was conducted to make clear the major intake route of DDT in Bangladesh people to develop strategy and policy that could lead to a reduction in body burden especially in the reproductive age women. The concentrations of several POPs (DDT, PCBs, chlordanes, HCHs, HCB, and PeCB) were quantified in food items, human breast milk and house dust collected in Bangladesh in 2011-2012. Among the POPs analyzed in this study, DDT and its metabolites (ΣDDT) showed the highest concentration. The highest median ΣDDT concentration was found in meat (1.3-1100 ng g-1 wet weight) and house dust (30-1100 ng g-1 dry weight), and followed by human breast milk (20-55 ng g-1 wet weight). Estimated daily intake (EDI) was calculated using the DDT concentrations in food items. The highest intake of DDT was found in an infant and 99% of it was via breast milk feeding. DDT intake via consumption of beef accounted for 69% and 72% of that found in children and adults, respectively. The total EDI of DDT did not exceed the tolerable daily intake proposed by the WHO, but the EDI of p,p'-DDT exceeded the oral reference dose proposed by the US Environmental Protection Agency. Further research is required to clarify the reason for the high levels of DDT in beef, which seems to be the major intake route of DDT for women of reproductive age in Bangladesh.

A missense variant, rs373863828-A (p.Arg457Gln), of CREBRF and body mass index in Oceanic populations.

It has been suggested that a 'thrifty' genotype hypothesis can account for high prevalence of obesity in the island populations of Oceania. A recent genome-wide association study revealed that a missense variant, rs373863828-A (p.Arg457Gln), of the CREBRF gene (encoding CREB3 regulatory factor) was associated with an excessive increase in body mass index (BMI) in Samoans. In the present study, the association of rs373863828-A with an increase in BMI was examined in four Austronesian (AN)-speaking populations in Oceania. We found that rs373863828-A was frequently observed (frequency of 0.15) in Tongans (Polynesians), and was strongly associated with higher BMI (P=6.1 × 10-4). A single copy of the rs373863828-A allele increased BMI by 3.09 kg m-2 after adjustment of age and sex. No significant association was detected in the other three AN-speaking populations (Melanesians and Micronesians) living in Solomon Islands. This was probably due to the low allele frequency (0.02-0.06) of rs373863828-A as well as small sample size. The rs373863828-A allele was not found in both AN-speaking and non-AN-speaking Melanesians living in Papua New Guinea. Our results suggest that rs373863828-A of CREBRF, a promising thrifty variant, arose in recent ancestors of AN-speaking Polynesians.

Reduced morning cortisol concentration in saliva was associated with obesity: Evidence from community-dwelling adults in papua new guinea.

OBJECTIVES: This study investigated morning salivary cortisol concentration in relation to total body fat composition among community-dwelling Papua New Guinean adults. METHODS: In addition to demographic and anthropometric measurements, saliva was collected in a single morning from 478 residents in Eastern Highlands Province and Madang Province. RESULTS: After adjusting for age, region, and occupation, the morning salivary cortisol concentration was significantly negatively correlated with body mass index among men (B = -0.01, P < 0.05) and women (B = -0.013, P < 0.05), and waist circumference (B = -0.007, P < 0.05), waist-to-hip-ratio (B = -1.214, P < 0.05), and subscapular-to-triceps skinfold-thickness ratio (B = -0.045, P < 0.05) among men. Men with total or abdominal body fat mass known for elevated risk of non-communicable diseases displayed lower cortisol compared to men without such risk. CONCLUSIONS: Papua New Guinean adults with increased accumulation of body fat showed reduced cortisol concentration in morning saliva. Am. J. Hum. Biol. 28:587-590, 2016. © 2016 Wiley Periodicals, Inc.

Non-monotonic relationships between arsenic and selenium excretion and its implication on arsenic methylation pattern in a Bangladeshi population.

The toxicity of arsenic differs markedly between individuals and populations, which might be related to the metabolism (methylation) of inorganic arsenic (As), as well as the selenium (Se) nutritional status. Urinary excretion of As (u-As) and Se (u-Se) was examined in an adult population (n=128) living in an As-contaminated area in Bangladesh. Although there was a significant negative correlation between u-Se and u-As (median 137; range 49-927 µg/g creatinine), closer examination revealed a non-monotonous relationship between them. A quadratic curve with an axis of As at 155 µg/g Cre gave a better fit, and u-As and u-Se were positively or negatively correlated depending on whether the As concentration was lower or higher than 155 µg As/g Cre, respectively. Likewise, the relationships between the As methylation pattern and glutathione-S-transferase (GST) polymorphism, body mass index (BMI), and u-Se differed depending on the u-As range; i.e., higher or lower than 155 µg/g Cre. Although we did not determine the causal mechanism for these observations, the non-monotonic relationship between As exposure and the variables examined suggested the existence of a threshold at which the handling of As by human body is qualitatively changed. The possible importance of Se nutrition for As toxicity is also discussed.

Arsenic contamination in groundwater and its effects on adolescent intelligence and social competence in Bangladesh with special reference to daily drinking/cooking water intake.

OBJECTIVE: The present study aims to investigate the relationship between arsenic (As) exposure and intelligence quotient (IQ) or social competence (SC) of Bangladeshi adolescents (aged 14 or 15 years) in Sonargaon thana. METHODS: Information about socioeconomic status (SES) was collected as confounding factors. To evaluate the relative contribution of As sources to total As intake, the As concentrations in urine and drinking/cooking water, and the amount of water added in cooking, were assessed on site using a food frequency questionnaire (FFQ). RESULTS: The results confirmed that As exposure was essential to lower adolescent IQ or SC because they were negatively associated with As exposure after controlling for SES (particularly household income). Except for cooking water, the amount of drinking water varied with season and appeared to be the major As source because the As concentration in water was generally correlated with the As concentration in urine, and they were related to lower IQ or SC (even after controlling for SES). The FFQ survey revealed that rice was consumed the most frequently (more than once daily), followed by daal (bean) soup and nonleafy vegetables, but fish, meat, and eggs were consumed approximately once a week. Water intake per meal from cooked rice was estimated to be 616 mL/person, followed by bean soup (258 mL/person) and cooked vegetables (82 mL/person). CONCLUSIONS: Our results suggest that water used for cooking might be an important source of As, and the cooking process can affect the amount of As in cooked food.

Nutritional status and functional capacity of community-dwelling elderly in Southern Laos.

OBJECTIVES: The aim of this study was to assess the nutritional status and functional capacity of 144 community-dwelling elderly in three rural ethnic groups, namely, the Oy, the Brau and the Lao, of southern Laos. METHODS: The Mini nutritional assessment (MNA) questionnaire and Determine Your Nutritional Health checklist were used to assess nutritional status. The Barthel Activities of Daily Living questionnaire and Lawton and Brody's Instrumental Activities of Daily Living questionnaire were used to assess the functional capacity of the respondents. RESULTS: The MNA score results indicated that 92.5 % of Oy respondents, 85.4 % of Brau respondents and 60 % of Lao respondents were malnourished. Analysis of variance tests showed that the MNA scores of the Oy and Lao ethnic groups and of the Brau and Lao ethnic groups were significantly different ( both p < 0.01), but that there was no significant difference between the MNA scores of the Oy and Brau ethnic groups (p > 0.05). In terms of functional capacity, 47.2 % of Oy respondents, 43.9 % of Brau respondents and 20 % of Lao respondents had limitations in their activities of daily living, whereas 98.1 % of Oy respondents, 97.6 % of Brau respondents and 86 % of Lao respondents had limitations in their instrumental activities of daily living. Body mass index, reduced appetite, number of meals consumed daily and presence of common diseases predicted nutritional status in all three ethnic groups; the remaining factors differed by ethnicity. This result implies that ethnic differences and other factors, such as location of the village, services, resources within the village and respondents' lifestyles, can affect nutritional status. CONCLUSIONS: Because predictors of nutritional status varied by ethnicity, there is a need for area-specific interventions aimed at improving the quality of life of the elderly in these areas.

A consecutive study on arsenic exposure and intelligence quotient (IQ) of children in Bangladesh.

OBJECTIVE: In a recent cross-sectional investigation, we reported the intellectual function of adolescents (aged 14 and 15 years) in Bangladesh who had been exposed to arsenic (As). Here, we report a consecutive investigation on the intelligence quotient (IQ) of 408 children who are living in the Sonargoan Thana of Bangladesh (two age groups: 9 and 10 years; 4 and 5 years) were exposed to high levels of As in the groundwater. METHODS: Urine and water samples were collected to assess As exposure. The IQ of the children was estimated using the Raven's Standard Progressive Matrices and the Kaufman Brief Intelligence Test. Information on parents' socioeconomic status (SES) was collected as confounding factors. RESULTS: The results indicate that As exposure was responsible for a lower IQ. The concentration of urinary As ([As]u) was associated with reduced intellectual function in a dose-response manner. A stronger association was found between reduced intellectual function (IQ) and [As]u than the level of As in the drinking water [As]w. There was no association between verbal IQ scores and [As]u of children in early childhood (aged 4 and 5 years). CONCLUSION: Based on these results, we conclude that current levels of As in the urine ([As]u), which we considered to reflect recent exposure to As from all possible sources, including groundwater, food, among others, were negatively associated to the IQ of the children tested, and that this adverse effect of As may also gradually accumulate over time among the poor.

Association of ADRB2 polymorphism with triglyceride levels in Tongans.

BACKGROUND: Our previous study demonstrated that the A-allele of the single nucleotide polymorphism (SNP) rs34623097 located in the upstream region of the ß2 adrenergic receptor gene (ADRB2) is significantly associated with risk for obesity in Oceanic populations. METHODS: To investigate whether the ADRB2 polymorphisms explain part of the individual differences in lipid mobilization, energy expenditure and glycogen breakdown, the associations of 10 ADRB2 SNPs with total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol and triglyceride levels were examined in 128 adults in Tonga. RESULTS: A multiple linear regression analysis adjusted for age, sex, and body mass index revealed that rs34623097 was significantly associated with triglyceride levels (P-value = 0.037). A copy of the rs34623097-A allele increased serum triglyceride levels by 70.1 mg/dL (0.791 mmol/L). None of the ADRB2 SNPs showed a significant association with total-cholesterol, high-density lipoprotein cholesterol, or low-density lipoprotein cholesterol. CONCLUSIONS: In a Tongan population, a SNP located in the upstream region of ADRB2 is associated with triglyceride levels independent of body mass index.

Hypertension-susceptibility gene prevalence in the Pacific Islands and associations with hypertension in Melanesia.

Human essential hypertension is partly caused by genetic factors. Angiotensinogen (AGT), G-protein ß3-subunit (GNB3) and cytochrome P450 3A5 (CYP3A5) are candidate hypertension susceptibility genes and risk alleles at these loci have been thought to arise owing to human adaptation to climatic changes following the migration out-of-Africa. This study aimed to reveal the frequencies of hypertension-susceptibility genotypes in Pacific Island populations and associations of these single-nucleotide polymorphisms (SNPs) to hypertension. Genotyping was conducted for 804 individuals from Melanesian, Micronesian and Polynesian populations at SNPs in the genes encoding AGT (rs699, rs5049 and rs5051), GNB3 (rs5443) and CYP3A5*1/*3 (rs776746). Associations between these SNPs and hypertension were tested for 383 Melanesian Solomon Islanders. We found that the A/A genotype at rs5049 was a risk factor for hypertension (P=0.025) in the Melanesian Solomon Islanders; three SNPs for AGT were in linkage disequilibrium. The ancestral alleles of rs699, rs5051 and rs776746, and the derived allele of rs5443 were as frequent in the populations surveyed here as in other equatorial populations. Although other polymorphisms associated with hypertension and additional populations remain to be studied, these findings suggest that the Pacific Islanders' susceptibility to hypertension arose because of human migration and adaptation.

Testing the thrifty gene hypothesis: the Gly482Ser variant in PPARGC1A is associated with BMI in Tongans.

BACKGROUND: the thrifty gene hypothesis posits that, in populations that experienced periods of feast and famine, natural selection favoured individuals carrying thrifty alleles that promote the storage of fat and energy. Polynesians likely experienced long periods of cold stress and starvation during their settlement of the Pacific and today have high rates of obesity and type 2 diabetes (T2DM), possibly due to past positive selection for thrifty alleles. Alternatively, T2DM risk alleles may simply have drifted to high frequency in Polynesians. To identify thrifty alleles in Polynesians, we previously examined evidence of positive selection on T2DM-associated SNPs and identified a T2DM risk allele at unusually high frequency in Polynesians. We suggested that the risk allele of the Gly482Ser variant in the PPARGC1A gene was driven to high frequency in Polynesians by positive selection and therefore possibly represented a thrifty allele in the Pacific. METHODS: here we examine whether PPARGC1A is a thrifty gene in Pacific populations by testing for an association between Gly482Ser genotypes and BMI in two Pacific populations (Maori and Tongans) and by evaluating the frequency of the risk allele of the Gly482Ser variant in a sample of worldwide populations. RESULTS: we find that the Gly482Ser variant is associated with BMI in Tongans but not in Maori. In a sample of 58 populations worldwide, we also show that the 482Ser risk allele reaches its highest frequency in the Pacific. CONCLUSION: the association between Gly482Ser genotypes and BMI in Tongans together with the worldwide frequency distribution of the Gly482Ser risk allele suggests that PPARGC1A remains a candidate thrifty gene in Pacific populations.

Knowledge, attitudes and practices relevant to malaria control in remote island populations of manus, papua new Guinea.

A community-based cross-sectional survey of 262 participants in four island communities of Manus, Papua New Guinea was conducted using a structured questionnaire to examine possible factors of malaria prevalence, including education experiences, knowledge, attitudes, and preventive behaviors, in relation to antimalarial antibody titers. Bivariate and multivariate analyses revealed that micro-environmental conditions caused inter-community differences in malaria prevalence. Ninety-nine percent of the subject villagers recognized mosquito bites as a cause of malaria transmission, which explains the high possession rate of bednets. There was a significant correlation between malaria education experience at schools and knowledge (p < 0.01) and between knowledge and bednet use (p < 0.05). However, regular bednet users were only 35% of the total, due primarily to feelings of discomfort, heat, and stuffiness inside the bednet. Villagers' behavior of consulting an aid post orderly (APO) in case of high fever significantly lowered the titer level (p < 0.05), while their bednet use did not. This unexpected result was attributable to inappropriate bednet use and to daily living patterns, including both subsistence and social activities. We conclude that information regarding lifestyles and attitudes toward bednet use as well as malaria education experience at schools are particularly important for practical malaria prevention.

The Q223R polymorphism in LEPR is associated with obesity in Pacific Islanders.

Various Pacific Island populations have experienced a marked increase in the prevalence of obesity in past decades. This study examined the association of a promoter polymorphism of the leptin gene (LEP), G-2548A (rs7799039), and two non-synonymous single nucleotide polymorphisms of the leptin receptor gene (LEPR), K109R (rs1137100) and Q223R (rs1137101), with body weight, body mass index (BMI) and obesity (BMI > or = 30) in Pacific Islanders. A total of 745 Austronesian (AN)-speaking participants were analyzed after adjusting for age, gender, and population differences. The results revealed that carriers of the 223Q alleles of LEPR had significantly higher body weight (P = 0.0009) and BMI (P = 0.0022) than non-carriers (i.e., 223R homozygotes); furthermore, the 223Q carriers also had a signiWcantly higher risk of obesity in comparison to non-carriers (P = 0.0222). The other two polymorphisms, G-2548A and K109R, were associated with neither body weight, BMI, nor obesity. The 223Q allele was widely found among the AN-speaking study subjects, thus suggesting that the LEPR Q223R polymorphism is one of the factors contributing to the high prevalence of obesity in the Pacific Island populations.

Gene flow and natural selection in oceanic human populations inferred from genome-wide SNP typing.

It is suggested that the major prehistoric human colonizations of Oceania occurred twice, namely, about 50,000 and 4,000 years ago. The first settlers are considered as ancestors of indigenous people in New Guinea and Australia. The second settlers are Austronesian-speaking people who dispersed by voyaging in the Pacific Ocean. In this study, we performed genome-wide single-nucleotide polymorphism (SNP) typing on an indigenous Melanesian (Papuan) population, Gidra, and a Polynesian population, Tongans, by using the Affymetrix 500K assay. The SNP data were analyzed together with the data of the HapMap samples provided by Affymetrix. In agreement with previous studies, our phylogenetic analysis indicated that indigenous Melanesians are genetically closer to Asians than to Africans and European Americans. Population structure analyses revealed that the Tongan population is genetically originated from Asians at 70% and indigenous Melanesians at 30%, which thus supports the so-called Slow train model. We also applied the SNP data to genome-wide scans for positive selection by examining haplotypic variation and identified many candidates of locally selected genes. Providing a clue to understand human adaptation to environments, our approach based on evolutionary genetics must contribute to revealing unknown gene functions as well as functional differences between alleles. Conversely, this approach can also shed some light onto the invisible phenotypic differences between populations.

FTO polymorphisms in oceanic populations.

It has been suggested that Neel's "thrifty genotype" model may account for high body weights in some Oceanic populations, which presumably arose in modern times. In European populations, common variants (rs1421085-C, rs17817449-G, and rs9939609-A) in the fat mass and obesity (FTO associated) were recently found to be associated with body mass index (BMI) or obesity. In this study, we investigated the population frequencies of these variants in six Oceanic populations (Melanesians, Micronesians, and Polynesians) and tested for an association with BMI. Unlike European populations, the Oceanic populations displayed no significant association between the FTO polymorphisms and BMI. These variants were in strong linkage disequilibrium. The population frequencies ranged between 4.2 and 30.3% in the six Oceanic populations, and were similar to those in southeast and east Asian populations. Our study of the FTO polymorphisms has generated no evidence to support the thrifty genotype hypothesis for Oceanic populations.

Dermatological and nutritional/growth effects among children living in arsenic-contaminated communities in rural Bangladesh.

While many reports have outlined the health risk of chronic arsenic exposure on adult populations, relatively little is known about the effects on children. We have examined the effects of chronic arsenic exposure through consumption of contaminated groundwater among 241 children (age 4-15 yr) living in two rural villages in northern Bangladesh. The arsenic concentrations of the tubewell waters ranged from less than detection limit to 535 ng/mL, and in 72 of 241 (30%) tubewells, the water arsenic concentration exceeded 50 ng/mL, the provisional guideline of Bangladesh. Approximately half of the examined children exhibited dermatological symptoms with relatively obscured dose-response relationship; an observation suggesting that the children were no more susceptible to the dermatological effects of arsenic than the adults living in the same communities. Proportion of the children with lower BMI significantly increased with increasing arsenic exposure level; the dose-response relationship was consistently observed among the subgroups. These results suggested that while mild dermatological manifestations, potentially associated with arsenic exposure, could be found as much as half of the children, nutritional status of the children, evaluated by BMI, might be a sensitive endpoint than the dermatological manifestations among children in this area.

Brief communication: mitochondrial DNA variation suggests extensive gene flow from Polynesian ancestors to indigenous Melanesians in the northwestern Bismarck Archipelago.

Archaeological, linguistic, and genetic studies show that Austronesian (AN)-speaking Polynesian ancestors came from Asia/Taiwan to the Bismarck Archipelago in Near Oceania more than 3,600 years ago, and then expanded into Remote Oceania. However, it remains unclear whether they extensively mixed with indigenous Melanesians who had populated the Bismarck Archipelago before their arrival. To examine the extent of admixture between Polynesian ancestors and indigenous Melanesians, mitochondrial DNA (mtDNA) variations in the D-loop region and the cytochrome oxidase and lysine transfer RNA (COII/tRNA(Lys)) intergenic 9-bp deletion were analyzed in the following three Oceanian populations: 1) Balopa Islanders as AN-speaking Melanesians living in the northwestern end of the Bismarck Archipelago, 2) Tongans as AN-speaking Polynesians, and 3) Gidra as non-Austronesian-speaking Melanesians in the southwestern lowlands of Papua New Guinea. Phylogenetic analysis of mtDNA sequences revealed that more than 60% of mtDNA sequences in the Balopa Islanders were very similar to those in Tongans, suggesting an extensive gene flow from Polynesian ancestors to indigenous Melanesians. Furthermore, analysis of pairwise difference distributions for the D-loop sequences with the 9-bp deletion and the Polynesian motif (i.e., T16217C, A16247G, and C16261T) suggested that the expansion of Polynesian ancestors possessing these variations occurred approximately 7,000 years ago.