Association between Drinking Water Nitrate and Adverse Reproductive Outcomes: A Systematic PRISMA Review

Nitrate contamination in drinking water and adverse reproductive and birth outcomes: a systematic review and meta-analysis

Exposure to low levels of nitrate in drinking water may have adverse reproductive effects. We reviewed evidence about the association between nitrate in drinking water and adverse reproductive outcomes published to November 2022. Randomized trials, cohort or case-control studies published in English that reported the relationship between nitrate intake from drinking water and the risk of perinatal outcomes were included. Random-effect models were used to pool data. Three cohort studies showed nitrate in drinking water is associated with an increased risk of preterm birth (odds ratio for 1 mg/L NO₃-N increased (OR₁) = 1.01, 95% CI 1.00, 1.01, I² = 23.9%, 5,014,487 participants; comparing the highest versus the lowest nitrate exposure groups pooled OR (OR_p) = 1.05, 95% CI 1.01, 1.10, I² = 0%, 4,152,348 participants). Case-control studies showed nitrate in drinking water may be associated with the increased risk of neural tube defects OR₁ = 1.06, 95% CI 1.02, 1.10; 2 studies, 2196 participants; I² = 0%; and OR_p = 1.51, 95% CI 1.12, 2.05; 3 studies, 1501 participants; I² = 0%). The evidence for an association between nitrate in drinking water and risk of small for gestational age infants, any birth defects, or any congenital heart defects was inconsistent. Increased nitrate in drinking water may be associated with an increased risk of preterm birth and some specific congenital anomalies. These findings warrant regular review as new evidence becomes available.

Drinking water nitrate and risk of pregnancy loss: a nationwide cohort study

BACKGROUND

Nitrate contamination is seen in drinking water worldwide. Nitrate may pass the placental barrier. Despite suggestive evidence of fetal harm, the potential association between nitrate exposure from drinking water and pregnancy loss remains to be studied. We aimed to investigate if nitrate in drinking water was associated with the risk of pregnancy loss.

METHODS

We conducted a nationwide cohort study of 100,410 pregnancies (enrolled around gestational week 11) in the Danish National Birth Cohort (DNBC) during 1996-2002. Spontaneous pregnancy losses before gestational week 22 were ascertained from the Danish National Patient Registry and DNBC pregnancy interviews. Using the national drinking water quality-monitoring database Jupiter, we estimated the individual and time-specific nitrate exposure by linking geocoded maternal residential addresses with water supply areas. The nitrate exposure was analyzed in spline models using a log-transformed continuous level or classified into five categories. We used Cox proportional hazards models to estimate associations between nitrate and pregnancy loss and used gestational age (days) as the time scale, adjusting for demographic, health, and lifestyle variables.

RESULTS

No consistent associations were found when investigating the exposure as a categorical variable and null findings were also found in trimester specific analyses. In the spline model using the continuous exposure variable, a modestly increased hazard of pregnancy loss was observed for the first trimester at nitrate exposures between 1 and 10 mg/L, with the highest. adjusted hazard ratio at 5 mg/L of nitrate of 1.16 (95% CI: 1.01, 1.34). This trend was attenuated in the higher exposure ranges.

CONCLUSION

No association was seen between drinking water nitrate and the risk of pregnancy loss when investigating the exposure as a categorical variable. When we modelled the exposure as a continuous variable, a dose-dependent association was found between drinking water nitrate exposure in the first trimester and the risk of pregnancy loss. Very early pregnancy losses were not considered in this study, and whether survival bias influenced the results should be further explored.

Assessment of sodium nitrate (NaNO3) effects on the reproductive system, liver, pancreas and kidney of male rats

Nitrate (NO₃) toxicity is a serious global issue that results in impairment of physiological systems of our body. The present study aimed to investigate the effects of different concentration of NaNO₃ (10, 100, 500 and 1000 mg/kg bw) on the male reproductive system, liver, kidney and pancreas. Adult male Wistar rats were divided into five groups of five animals each (n = 5). The first group served as controls. The second, third, fourth and fifth groups of rat were orally intubated with 10, 100, 500 and 1000 mg/kg bw of NaNO₃ for 52 days. After the treatment period, the rats were sacrificed and NO₃ induced alterations on selected organs were assessed. There was a dose dependent decrease in sperm motility, serum concentration of testosterone, body weight and organ weight, and increase in abnormal sperm morphology in the NaNO₃ treated groups compared with the controls. Further, histological analysis confirmed that NO₃ induced toxicity. Shrunken seminiferous tubules and loss of spermatids in testes, shrinkage of acinar cells of the pancreas, sinusoidal congestion and necrosis in the liver, atrophy of glomeruli and congestion of renal tubules of the kidney were the histological alterations observed in rats treated with100 and 500 mg/kg NaNO₃. However, 100% mortality was observed in rats treated with 1000 mg/kg NaNO₃. The present study clearly demonstrated the toxic effects of NaNO₃ on both the reproductive system and other organs of the body. The study might inform human studies; where in the chances of male infertility may be more a problem for individuals in areas with NO₃-rich ground water.

Nitrate in Drinking Water and Time to Pregnancy or Medically Assisted Reproduction in Women and Men: A Nationwide Cohort Study in the Danish National Birth Cohort

Purpose

No studies have investigated if drinking water nitrate affects human fecundity. Experimental studies point at detrimental effects on fetal development and on female and male reproduction. This cohort study aimed to explore if female and male preconception and long-term exposure to nitrate in drinking water was associated with fecundability measured as time to pregnancy (TTP) or use of medically assisted reproduction (MAR) treatment.

Methods

The study population consisted of pregnant women recruited in their first trimester in 1996–2002 to the Danish National Birth Cohort. Preconception drinking-water nitrate exposure was estimated for the pregnant women (89,109 pregnancies), and long-term drinking water nitrate exposure was estimated from adolescence to conception for the pregnant women (77,474 pregnancies) and their male partners (62,000 pregnancies) by linkage to the national drinking water quality-monitoring database Jupiter. Difference in risk of TTP >12 months or use of MAR treatment between five exposure categories and log-transformed continuous models of preconception and long-term nitrate in drinking water were estimated. Binominal regression models for risk ratios (RR) were adjusted for age, occupation, education, population density, and lifestyle factors.

Results

Nitrate in drinking water (median preconception exposure: 1.9 mg/L; median long-term exposure: 3.3 mg/L) was not associated with TTP >12 months or use of MAR treatment, neither in the categorical nor in the continuous models.

Conclusion

We found no association between preconception or long-term exposure to drinking water nitrate and fecundability.

Influence of Fruit and Vegetable Consumption on Antioxidant Status and Semen Quality: A Cross-Sectional Study in Adult Men

The influence of fruit and vegetable consumption on semen quality by reducing oxidative stress is inconsistent. Thus, the association between the consumption of these products, antioxidant status, and semen quality was investigated in 90 men aged 18–40. The consumption of fruit and vegetables was collected using the 3-day food record method. Antioxidant status: total antioxidant capacity in semen (TAC-s) and blood (TAC-b), blood superoxide dismutase (SOD-b), glutathione reductase (GR-b), glutathione peroxidase (GPx-b), catalase (CAT-b) activity, and malondialdehyde concentration in blood (MDA-b) were measured. Sperm concentration, leukocytes in the ejaculate, vitality, motility, and sperm morphology were examined using computer-aided semen analysis (CASA). The consumption of fruit and vegetables was positively correlated with sperm concentration, vitality, motility, TAC-s, TAC-b, and SOD-b activity. The TAC-s and TAC-b were positively related to motility, TAC-s was inversely correlated with sperm tail defects. The SOD-b activity was positively correlated with vitality, motility, sperm morphology, and inversely with sperm tail defects and leukocytes in the ejaculate. Compared to the men in the first quartile of fruit and vegetable consumption (<318 g/day), those in the highest quartile (>734 g/day) had the highest sperm concentration, vitality, motility, TAC-s, TAC-b, GPx-b activity, and the lowest MDA-b concentration (based on multivariate regression models). A high consumption of fruit and vegetables may positively influence selected sperm quality parameters by improving the antioxidant status of semen and blood.