UV Exposure and Racial Disparities in Birth Outcomes
UV Exposure and Racial Disparities in Birth Outcomes
In 2007, 11.8% of all singleton births to black mothers were LBW, compared with 5.3% of births to white mothers. A total of 17.6% of black women gave birth preterm (not medically induced) compared with 10.8% of white women. The racial disparity in the incidence rates of LBW and PTB was significantly higher in southern states, largely driven by higher rates of adverse birth outcomes among black women in the South (for blacks, LBW = 12.1% in southern states vs. 9.3% in northern states, P < 0.0001; for whites, LBW = 5.8% in southern states vs. 4.9% in northern states, P = 0.002; for blacks, PTB = 18.4% in southern states vs. 14.7% in northern states, P < 0.0001; for whites, PTB = 11.9% in southern states vs. 9.9% in northern states, P = 0.001) (Figure 1) There was a significant environmental gradient in population size, with a higher number of women giving birth in southern states overall (P < 0.001).
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Figure 1.
Variation in A) poverty rates, B) ultraviolet (UV) light exposure, and C) preterm birth (PTB) disparity across the United States. Poverty rate data from the Kaiser Family Foundation State Facts, 2009 (47); UV light exposure data from the National Oceanic and Atmospheric Administration, 2007 (41); and PTB data from the Centers for Disease Control and Prevention, 2007 (43).
States with greater income inequality had greater disparity in birth outcomes across the UV light spectrum (Figure 2). In addition, smoking, obesity, Gini coefficient, poverty rate, UV index value, average temperature, and number of clear days in 2007 were all significantly higher in states at lower latitudes, whereas health care spending was significantly lower in those states (Table 1). Of the economic, health, and environmental variables, poverty rate, Gini coefficient, latitude, mean annual temperature, and obesity were all significantly correlated with disparity in the rates of LBW (Table 2). Gini coefficient, latitude, and temperature were all significantly correlated with disparity in the rates of PTB.
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Figure 2.
Relationships between income inequality, as indexed by a higher Gini coefficient, and disparities in A) low birth weight (LBW) and B) preterm birth (PTB) across tertiles of the ultraviolet (UV) index spectrum in the United States. Values represent means (standard deviations). UV light exposure data from the National Oceanic and Atmospheric Administration, 2007 (41); LBW and PTB data from the Centers for Disease Control and Prevention, 2007 (43); and Gini coefficient data from the US Census Bureau, 2007 (49).
The racial disparity in LBW was greater among women living in areas with higher UV light exposure and greater income inequality (for higher UV light exposure, β = 0.007 (standard error (SE), 0.002), P = 0.002; for Gini coefficient, β = 0.34 (SE, 0.11), P = 0.003; adjusted R = 0.37). In this model, a 1-point increase in UV score was associated with a 0.7% greater racial disparity in LBW between black and white women, whereas a 0.1-point increase in Gini coefficient was associated with a 3.4% greater racial disparity in LBW between these groups. When comparing the relationships among UV light exposure, Gini coefficient, and LBW between black and white women, we found that black women were more sensitive to the negative effects of UV light exposure and income inequality than were white women (for UV light exposure in black women, β = 0.01 (SE, 0.002), P < 0.001; for Gini coefficient in black women, β = 0.26 (SE, 0.12), P = 0.04, adjusted R = 0.45; for UV light exposure in white women, β = 0.005 (SE, 0.001), P < 0.001; for Gini coefficient in white women, β = −0.08 (SE, 0.06), P = 0.17, adjusted R = 0.30) (Figure 3).
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Figure 3.
Relationship between disparity of the incidence of A) low birth weight and B) preterm birth across ultraviolet (UV) index scores for non-Hispanic blacks and non-Hispanic whites in the United States. UV light exposure data from the National Oceanic and Atmospheric Administration, 2007 (41); low birth weight and preterm birth data from the Centers for Disease Control and Prevention, 2007 (43).
Disparity in PTB was similarly highest in areas with greater UV light exposure and income inequality (for UV light exposure, β = 0.006 (SE, 0.003), P = 0.03; for Gini coefficient, β = 0.30 (SE, 0.15), P = 0.05, adjusted R = 0.19). Each 1-point increase in UV index value was associated with a 0.6% greater racial disparity in PTB, whereas each 0.1-point increase in Gini coefficient was associated with a 3.0% greater racial disparity in PTB. UV light exposure was more strongly associated with PTB risk among black women than among white women, whereas Gini coefficient was unrelated when looking at PTB risk within each racial group (for UV light exposure in blacks, β = 0.02 (SE, 0.003), P < 0.001, adjusted R = 0.45; for Gini coefficient in whites, β = 0.20 (SE, 0.16), P = 0.21, adjusted R = 0.45; for UV light exposure in whites, β = 0.01 (SE, 0.002), P < 0.001; for Gini coefficient in whites, β = −0.09 (SE, 0.11), P = 0.40, adjusted R = 0.34).
Results
In 2007, 11.8% of all singleton births to black mothers were LBW, compared with 5.3% of births to white mothers. A total of 17.6% of black women gave birth preterm (not medically induced) compared with 10.8% of white women. The racial disparity in the incidence rates of LBW and PTB was significantly higher in southern states, largely driven by higher rates of adverse birth outcomes among black women in the South (for blacks, LBW = 12.1% in southern states vs. 9.3% in northern states, P < 0.0001; for whites, LBW = 5.8% in southern states vs. 4.9% in northern states, P = 0.002; for blacks, PTB = 18.4% in southern states vs. 14.7% in northern states, P < 0.0001; for whites, PTB = 11.9% in southern states vs. 9.9% in northern states, P = 0.001) (Figure 1) There was a significant environmental gradient in population size, with a higher number of women giving birth in southern states overall (P < 0.001).
(Enlarge Image)
Figure 1.
Variation in A) poverty rates, B) ultraviolet (UV) light exposure, and C) preterm birth (PTB) disparity across the United States. Poverty rate data from the Kaiser Family Foundation State Facts, 2009 (47); UV light exposure data from the National Oceanic and Atmospheric Administration, 2007 (41); and PTB data from the Centers for Disease Control and Prevention, 2007 (43).
States with greater income inequality had greater disparity in birth outcomes across the UV light spectrum (Figure 2). In addition, smoking, obesity, Gini coefficient, poverty rate, UV index value, average temperature, and number of clear days in 2007 were all significantly higher in states at lower latitudes, whereas health care spending was significantly lower in those states (Table 1). Of the economic, health, and environmental variables, poverty rate, Gini coefficient, latitude, mean annual temperature, and obesity were all significantly correlated with disparity in the rates of LBW (Table 2). Gini coefficient, latitude, and temperature were all significantly correlated with disparity in the rates of PTB.
(Enlarge Image)
Figure 2.
Relationships between income inequality, as indexed by a higher Gini coefficient, and disparities in A) low birth weight (LBW) and B) preterm birth (PTB) across tertiles of the ultraviolet (UV) index spectrum in the United States. Values represent means (standard deviations). UV light exposure data from the National Oceanic and Atmospheric Administration, 2007 (41); LBW and PTB data from the Centers for Disease Control and Prevention, 2007 (43); and Gini coefficient data from the US Census Bureau, 2007 (49).
The racial disparity in LBW was greater among women living in areas with higher UV light exposure and greater income inequality (for higher UV light exposure, β = 0.007 (standard error (SE), 0.002), P = 0.002; for Gini coefficient, β = 0.34 (SE, 0.11), P = 0.003; adjusted R = 0.37). In this model, a 1-point increase in UV score was associated with a 0.7% greater racial disparity in LBW between black and white women, whereas a 0.1-point increase in Gini coefficient was associated with a 3.4% greater racial disparity in LBW between these groups. When comparing the relationships among UV light exposure, Gini coefficient, and LBW between black and white women, we found that black women were more sensitive to the negative effects of UV light exposure and income inequality than were white women (for UV light exposure in black women, β = 0.01 (SE, 0.002), P < 0.001; for Gini coefficient in black women, β = 0.26 (SE, 0.12), P = 0.04, adjusted R = 0.45; for UV light exposure in white women, β = 0.005 (SE, 0.001), P < 0.001; for Gini coefficient in white women, β = −0.08 (SE, 0.06), P = 0.17, adjusted R = 0.30) (Figure 3).
(Enlarge Image)
Figure 3.
Relationship between disparity of the incidence of A) low birth weight and B) preterm birth across ultraviolet (UV) index scores for non-Hispanic blacks and non-Hispanic whites in the United States. UV light exposure data from the National Oceanic and Atmospheric Administration, 2007 (41); low birth weight and preterm birth data from the Centers for Disease Control and Prevention, 2007 (43).
Disparity in PTB was similarly highest in areas with greater UV light exposure and income inequality (for UV light exposure, β = 0.006 (SE, 0.003), P = 0.03; for Gini coefficient, β = 0.30 (SE, 0.15), P = 0.05, adjusted R = 0.19). Each 1-point increase in UV index value was associated with a 0.6% greater racial disparity in PTB, whereas each 0.1-point increase in Gini coefficient was associated with a 3.0% greater racial disparity in PTB. UV light exposure was more strongly associated with PTB risk among black women than among white women, whereas Gini coefficient was unrelated when looking at PTB risk within each racial group (for UV light exposure in blacks, β = 0.02 (SE, 0.003), P < 0.001, adjusted R = 0.45; for Gini coefficient in whites, β = 0.20 (SE, 0.16), P = 0.21, adjusted R = 0.45; for UV light exposure in whites, β = 0.01 (SE, 0.002), P < 0.001; for Gini coefficient in whites, β = −0.09 (SE, 0.11), P = 0.40, adjusted R = 0.34).
