Linear hair growth rates in preschool children

BACKGROUND

Human scalp hair is a validated bio-substrate for monitoring various exposures in childhood including contextual stressors, environmental toxins, prescription or non-prescription drugs. Linear hair growth rates (HGR) are required to accurately interpret hair biomarker concentrations.

METHODS

We measured HGR in a prospective cohort of preschool children (N = 266) aged 9-72 months and assessed demographic factors, anthropometrics, and hair protein content (HPC). We examined HGR differences by age, sex, race, height, hair pigment, and season, and used univariable and multivariable linear regression models to identify HGR-related factors.

RESULTS

Infants below 1 year (288 ± 61 μm/day) had slower HGR than children aged 2-5 years (p = 0.0073). Dark-haired children (352 ± 52 μm/day) had higher HGR than light-haired children (325 ± 50 μm/day; p = 0.0019). Asian subjects had the highest HGR overall (p = 0.016). Younger children had higher HPC (p = 0.0014) and their HPC-adjusted HGRs were slower than older children (p = 0.0073). Age, height, hair pigmentation, and HPC were related to HGR in multivariable regression models.

CONCLUSIONS

We identified age, height, hair pigment, and hair protein concentration as significant determinants of linear HGRs. These findings help explain the known hair biomarker differences between children and adults and aid accurate interpretation of hair biomarker results in preschool children.

IMPACT

Discovery of hair biomarkers in the past few decades has transformed scientific disciplines like toxicology, pharmacology, epidemiology, forensics, healthcare, and developmental psychology. Identifying determinants of hair growth in children is essential for accurate interpretation of hair biomarker results in pediatric clinical studies. Childhood hair growth rates define the time-periods of biomarker incorporation into growing hair, essential for interpreting the biomarkers associated with environmental exposures and the mind-brain-body connectome. Our study describes age-, sex-, and height-based distributions of linear hair growth rates and provides determinants of linear hair growth rates in a large population of children. Age, height, hair pigmentation, and hair protein content are determinants of hair growth rates and should be accounted for in child hair biomarkers studies. Our findings on hair protein content and linear hair growth rates may provide physiological explanations for differences in hair growth rates and biomarkers in preschool children as compared to adults.

Effects of Aging on Hair Color, Melanosomes, and Melanin Composition in Japanese Males and Their Sex Differences

In a previous study, we observed that the hair color of Japanese females darkens with age and that the causes of this are the increase in melanosome size, the amount of melanin, and the mol% of 5,6-dihydroxyindole (DHI) which has a high absorbance. In this study, we extended the same analyses to male hair to examine the sex differences in hair color, melanin composition, and melanosome morphology. Male hair also tended to darken with age, but it was darker than female hair in those of younger ages. Although there was no age dependence of DHI mol% in male hair, as with female hair, the melanosomes' sizes enlarged with age, the total melanin amount increased, and these findings were correlated with hair color. The analyses, considering age dependence, revealed that there were significant sex differences in the ratio of absorbance of dissolved melanin at the wavelength of 650 nm to 500 nm, in pheomelanin mol%, and in melanosome morphology parameters such as the minor axis. This may be the cause of the sex differences in hair color. Furthermore, the factors related to hair color were analyzed using all the data of the male and female hairs. The results suggested that total melanin amount, pheomelanin mol%, and DHI mol% correlated with hair color.

Estimation of the Frequency and Time of Human Exposure to Arsenic by Single Hair Analysis

Arsenic (As) and its compounds are widely used in many applications. Long-term exposure to As can cause acute and chronic poisoning. In severe cases, it can lead to adverse effects, such as gene mutation, cell cancer and fetal malformation. The objective of this study was to accurately estimate As exposure frequency and time. Quantitative analysis of As in single hairs obtained from APL (acute promyelocytic leukemia) patients treated with As₂O₃ was performed by LA-ICP-MS. An informative As concentration distribution profile of single hair was applied to estimate the As exposure frequency and time. As exposure frequency was estimated according to the number of As concentration peaks. As exposure time was estimated according to the hair growth length in combination with the hair growth rate. The validation results demonstrate that this method was more efficient than the traditional method; compared with the traditional method, which provides estimates in months, our model shortened the As exposure time estimate to the range of a few days, which considerably improved the inference accuracy. Therefore, these results can be used for forensic toxicology studies, environmental exposure monitoring, etc.

Hair to blood mercury concentration ratios and a retrospective hair segmental mercury analysis in the Northwest Territories, Canada

Concentrations of total mercury were measured in blood and hair samples collected as part of a human biomonitoring project conducted in First Nations communities of the Mackenzie Valley, Northwest Territories, Canada. Hair (n = 443) and blood (n = 276) samples were obtained from six communities in the Dehcho region and three communities in the Sahtú region of the Mackenzie Valley. The aim of this paper was to calculate hair to blood mercury ratios (for matched samples) and determine if: 1) ratios differed significantly between the two regions; 2) ratios differed from the 250:1 ratio proposed by the WHO; and, 3) point estimates of hair to blood mercury ratios could be used to estimate blood mercury concentrations. In addition, this paper aims to determine if there were seasonal patterns in hair mercury concentrations in these regions and if so, if patterns were related to among-season variability in fish consumption. The majority of mercury levels in hair and blood were below relevant health-based guidance values. The geometric mean hair (most recent segment) to blood mercury ratio (stratified by region) was 619:1 for the Dehcho region and 1220:1 for the Sahtú region. Mean log-transformed hair to blood mercury ratios were statistically significantly different between the two regions. Hair to blood ratios calculated in this study were far higher (2-5 times higher) than those typically reported in the literature and there was a large amount of inter-individual variation in calculated ratios (range: 114:1 to 4290:1). Using the 250:1 ratio derived by the World Health Organisation to estimate blood mercury concentrations from hair mercury concentrations would substantially over-estimate blood mercury concentrations in the studied regions. However, geometric mean site-specific hair to blood mercury ratios can provide estimates of measures of central tendency for blood mercury concentrations from hair mercury concentrations at a population level. Mercury concentrations were determined in segments of long hair samples to examine exposure of participants to mercury over the past year. Hair segments were assigned to six time periods and the highest hair mercury concentrations were generally observed in hair segments that aligned with September/October and November/December, whereas the lowest hair mercury concentrations were aligned with March/April and May/June. Mean log-transformed hair mercury concentrations were statistically significantly different between time periods. Between time periods (e.g., September/October vs. March/April), the geometric mean mercury concentration in hair differed by up to 0.22 μg/g, and the upper margins of mercury exposure (e.g., 95th percentile of hair mercury) varied by up to 0.86 μg/g. Results from self-reported fish consumption frequency questionnaires (subset of participants; n = 170) showed total fish intake peaked in late summer, decreased during the winter, and then increased during the spring. Visual assessment of results indicated that mean hair mercury concentrations followed this same seasonal pattern. Results from mixed effects models, however, indicated that variability in hair mercury concentrations among time periods was not best explained by total fish consumption frequency. Instead, seasonal trends in hair mercury concentrations may be more related to the consumption of specific fish species (rather than total wild-harvested fish in general). Future work should examine whether seasonal changes in the consumption of specific fish species are associated with seasonal changes in hair mercury concentrations.

The risk of missed abortion associated with the levels of tobacco, heavy metals and phthalate in hair of pregnant woman: A case control study in Chinese women

To assess the association between exposure to the tobacco, heavy metals and phthalate on early pregnancy and missed abortion.42 women with missed abortion and 57 matched controls (women with normal pregnancies) were recruited between March and May 2012, from the Department of Gynecology and Obstetrics, First Affiliated Hospital of Guangxi Medical University and the People Hospital of Guangxi Zhuang Autonomous Region. The questionnaire survey was carried on to learn about the basic conditions, as well as smoking history of all participants. The levels of tobacco, heavy metal, and phthalate exposure were compared between the 2 groups by measuring nicotine, cocaine, cadmium (Cd), manganese (Mn), plumbum (Pb) and dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), butyl benzyl phthalate (BBP), di-2-ethyl hexyl phthalate (DEHP) in the hair samples.Out results showed that significant differences in age (P = .042), premarital examination (P = .041), passive smoking (P = .021), and heavy metal exposure (P = .022) were found in the case group compared to the control. In addition, the concentration of nicotine (P = .037), cotinine (P = .018), Cd (P = .01), Pb (P = .038) and DEHP (P = .001) in the hair were significantly higher in the case group. Furthermore, logistic analysis revealed that age [Odds Ratio (OR) 1.172, 95% confidence interval (CI) 1.036-1.327], Cd (OR 8.931, 95% CI 2.003-39.811), Cotinine (OR 4.376, 95% CI 1.159-16.531), DEHP (OR 1.863, 95% CI 1.103-3.146) were important factors contributing to the missed abortion (P < .05).It was demonstrated that high gestational age, passive smoking, heavy metals, and the phthalate exposure were the risk factors for missed abortion, while the premarital health examination was a protective factor. Avoiding these harmful substances before getting pregnant and during the early stages of pregnancy, might help prevent missed abortions.

Hair follicle characteristics as early marker of Type 2 Diabetes

Type 2 Diabetes mellitus (DM2) includes a continuum of metabolic disorders characterized by hyperglycemia that causes several chronic long-term complications such as coronary artery disease, peripheral arterial disease, nephropathy, and neuropathy. The hair follicle could reveal signs of early vascular impairment, yet its relationship to early metabolic injuries has been largely ignored. We propose that in earlier stages of the continuum of DM2-related metabolic disorders, a group of susceptible patients who do not yet meet the diagnostic criteria to be considered as persons with DM2 may present chronic vascular impairment and end organ damage, including hair follicle damage, which can be evaluated to identify an early risk marker. This hypothesis is based in the association found between insulin resistance and alopecia in non-diabetic persons, and the hair loss on the lower limbs as a manifestation of long-term peripheral arterial disease among subjects with DM2. In order to test this hypothesis, studies are required to evaluate if hair follicle characteristics are related to and can predict hyperglycemic complications, and if they do so, which feature of the hair follicle, such as hair growth, best characterizes such DM2-related conditions. If this hypothesis were proven to be true, significant advances towards a personalized approach for early prevention strategies and management of DM2 would be made. By focusing on the hair follicles, early stages of metabolic-related organ damage could be identified using non-invasive low-cost techniques. In so doing, this approach could provide early identification of DM2-susceptible individuals and lead to the early initiation of adequate primary prevention strategies to reduce or avoid the onset of large internal organ damage.