Figure 1
Map of the distribution of standardized heights and weights of Japanese youth. Map of the distribution of the 25-year (1989–2013) average of standardized heights and weights of the following subject groups in each prefecture: (A) heights of 12-year-old boys, (B) weights of 12-year-old boys, (C) heights of 17-year-old boys, and (D) weights of 17-year-old boys [5, 6].
Table 1
Basic statistics for standardized heights and weights.
| Standardized Height | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Boys | Girls | |||||||||
| Age | 5 | 8 | 11 | 14 | 17 | 5 | 8 | 11 | 14 | 17 |
| Maximum | 0.214 | 0.218 | 0.237 | 0.219 | 0.166 | 0.221 | 0.223 | 0.226 | 0.158 | 0.121 |
| Akita | Akita | Akita | Akita | Akita | Akita | Aomori | Aomori | Akita | Akita | |
| Minimum | –0.261 | –0.246 | –0.135 | –0.171 | –0.305 | –0.202 | –0.133 | –0.100 | –0.306 | –0.323 |
| Okinawa | Okinawa | Yamaguchi | Miyazaki | Okinawa | Okinawa | Okinawa | Yamaguchi | Okinawa | Okinawa | |
| Mean | –0.009 | –0.006 | –0.001 | –0.008 | –0.011 | –0.003 | 0.001 | 0.004 | –0.012 | –0.013 |
| Median | –0.014 | 0.000 | –0.028 | –0.018 | –0.008 | –0.010 | –0.007 | –0.006 | –0.020 | –0.007 |
| Standardized Weight | ||||||||||
| Boys | Girls | |||||||||
| Age | 5 | 8 | 11 | 14 | 17 | 5 | 8 | 11 | 14 | 17 |
| Maximum | 0.234 | 0.295 | 0.289 | 0.262 | 0.220 | 0.242 | 0.293 | 0.255 | 0.229 | 0.195 |
| Aomori | Aomori | Aomori | Aomori | Akita | Aomori | Aomori | Aomori | Aomori | Akita | |
| Minimum | –0.133 | –0.106 | –0.157 | –0.158 | –0.139 | –0.135 | –0.099 | –0.099 | –0.107 | –0.254 |
| Okinawa | Yamaguchi | Shimane | Yamaguchi | Yamaguchi | Okinawa | Yamaguchi | Yamaguchi | Okinawa | Okinawa | |
| Mean | –0.001 | 0.008 | 0.003 | –0.002 | 0.002 | 0.003 | 0.013 | 0.011 | 0.011 | 0.014 |
| Median | –0.031 | –0.026 | –0.030 | –0.025 | –0.016 | –0.031 | –0.014 | –0.008 | –0.015 | 0.002 |
Figure 2
Distribution map of solar radiation and effective day length at 5000 lux in Japan. The fill in the mesh areas indicates (A) annual mean effective day length at 5000 lux (h/day), (B) effective day length at 5000 lux in June (h/day), (C) effective day length at 5000 lux in December (h/day), and (D) annual mean solar radiation (MJ/m2/day) [5, 6].
Table 2
Basic statistics for climatic variables.
| Effective day length of the longest month at 5000 lux (h/day) | Effective day length of the shortest month at 5000 lux (h/day) | |
|---|---|---|
| Maximum | 12.6 (Hokkaido: Jun) | 8.9 (Okinawa: Jan) |
| Minimum | 11.8 (Tokyo: May–July, Kanagawa: May–July) | 6.9 (Akita: Dec) |
| Mean | 12.02 | 8.08 |
| Median | 12.00 | 8.30 |
Table 3
Pearson’s correlation coefficients for the relationship between height, weight, and effective day length of the longest or shortest months.
| Height vs. effective day length of the longest month | Height vs. effective day length of the shortest month | Weight vs. effective day length of the longest month | Weight vs. effective day length of the shortest month | Height vs. weight | |
|---|---|---|---|---|---|
| Boys | |||||
| Age: 5 | 0.54** | –0.80** | 0.53* | –0.58** | 0.82** |
| 6 | 0.50* | –0.75** | 0.58** | –0.62** | 0.82** |
| 7 | 0.54* | –0.79** | 0.65** | –0.68** | 0.82** |
| 8 | 0.53* | –0.80** | 0.65** | –0.67** | 0.81** |
| 9 | 0.54** | –0.81** | 0.66** | –0.68** | 0.83** |
| 10 | 0.59** | –0.82** | 0.65** | –0.64** | 0.86** |
| 11 | 0.61** | –0.81** | 0.63** | –0.61** | 0.88** |
| 12 | 0.64** | –0.81** | 0.65** | –0.60** | 0.87** |
| 13 | 0.61** | –0.84** | 0.65** | –0.62** | 0.84** |
| 14 | 0.52* | –0.83** | 0.64** | –0.65** | 0.78** |
| 15 | 0.41* | –0.79** | 0.57** | –0.64** | 0.68** |
| 16 | 0.36 | –0.76** | 0.58** | –0.68** | 0.66** |
| 17 | 0.33 | –0.74** | 0.62** | –0.71** | 0.63** |
| Girls | |||||
| Age: 5 | 0.57** | –0.79** | 0.52* | –0.57** | 0.84** |
| 6 | 0.55** | –0.76** | 0.59** | –0.62** | 0.84** |
| 7 | 0.56** | –0.81** | 0.62** | –0.66** | 0.83** |
| 8 | 0.58** | –0.82** | 0.63** | –0.66** | 0.85** |
| 9 | 0.61** | –0.82** | 0.65** | –0.64** | 0.86** |
| 10 | 0.63** | –0.81** | 0.62** | –0.59** | 0.86** |
| 11 | 0.61** | –0.82** | 0.60** | –0.54** | 0.78** |
| 12 | 0.51* | –0.83** | 0.62** | –0.53* | 0.58** |
| 13 | 0.38 | –0.74** | 0.64** | –0.59** | 0.49* |
| 14 | 0.32 | –0.75** | 0.63** | –0.63** | 0.48* |
| 15 | 0.26 | –0.69** | 0.56** | –0.62** | 0.49* |
| 16 | 0.25 | –0.66** | 0.55** | –0.66** | 0.53* |
| 17 | 0.26 | –0.69** | 0.54** | –0.65** | 0.56** |
[i] ** p < 0.0001 * p < 0.005.
Table 4
Regression coefficients (standard errors) of predictors for height (boys).
| Boys | Predictors | Regression coefficient | Standard error | 95% CI Lower | 95% CI Upper | t | p | Adjusted R2 |
|---|---|---|---|---|---|---|---|---|
| Age: 5 | Weight | 0.57 | 0.07 | 0.44 | 0.70 | 8.66 | <0.001 | 0.876 |
| Longest5000 | –0.36 | 0.09 | –0.53 | –0.18 | –4.05 | <0.001 | ||
| Shortest5000 | –0.75 | 0.09 | –0.94 | –0.57 | –8.26 | <0.001 | ||
| 7 | Weight | 0.60 | 0.08 | 0.43 | 0.77 | 7.09 | <0.001 | 0.839 |
| Longest5000 | –0.43 | 0.10 | –0.63 | –0.22 | –4.17 | <0.001 | ||
| Shortest5000 | –0.73 | 0.11 | –0.94 | –0.51 | –6.83 | <0.001 | ||
| 9 | Weight | 0.63 | 0.07 | 0.49 | 0.78 | 8.95 | <0.001 | 0.890 |
| Longest5000 | –0.49 | 0.08 | –0.66 | –0.31 | –5.71 | <0.001 | ||
| Shortest5000 | –0.77 | 0.09 | –0.94 | –0.59 | –8.83 | <0.001 | ||
| 11 | Weight | 0.70 | 0.05 | 0.60 | 0.81 | 13.47 | <0.001 | 0.932 |
| Longest5000 | –0.36 | 0.07 | –0.50 | –0.22 | –5.28 | <0.001 | ||
| Shortest5000 | –0.66 | 0.07 | –0.80 | –0.53 | –10.05 | <0.001 | ||
| 13 | Weight | 0.64 | 0.05 | 0.53 | 0.74 | 12.12 | <0.001 | 0.933 |
| Longest5000 | –0.44 | 0.07 | –0.57 | –0.30 | –6.42 | <0.001 | ||
| Shortest5000 | –0.79 | 0.07 | –0.92 | –0.66 | –12.11 | <0.001 | ||
| 15 | Weight | 0.37 | 0.08 | 0.21 | 0.54 | 4.51 | <0.001 | 0.826 |
| Longest5000 | –0.65 | 0.10 | –0.85 | –0.44 | –6.21 | <0.001 | ||
| Shortest5000 | –1.06 | 0.11 | –1.28 | –0.84 | –9.55 | <0.001 | ||
| 17 | Weight | 0.30 | 0.11 | 0.09 | 0.51 | 2.85 | 0.007 | 0.760 |
| Longest5000 | –0.72 | 0.12 | –0.97 | –0.48 | –5.92 | <0.001 | ||
| Shortest5000 | –1.10 | 0.14 | –1.37 | –0.82 | –8.09 | <0.001 |
[i] Longest5000: Effective day length of the longest month at 5000 lux.
Shortest5000: Effective day length of the shortest month at 5000 lux.
Table 5
Regression coefficients (standard errors) of predictors for height (girls).
| Girls | Predictors | Regression coefficient | Standard error | 95% CI Lower | 95% CI Upper | T | p | Adjusted R2 |
|---|---|---|---|---|---|---|---|---|
| Age: 5 | Weight | 0.61 | 0.06 | 0.48 | 0.74 | 9.81 | <0.001 | 0.887 |
| Longest5000 | –0.28 | 0.08 | –0.45 | –0.11 | –3.36 | 0.002 | ||
| Shortest5000 | –0.67 | 0.09 | –0.85 | –0.49 | –7.70 | <0.001 | ||
| 7 | Weight | 0.59 | 0.08 | 0.43 | 0.75 | 7.45 | <0.001 | 0.854 |
| Longest5000 | –0.36 | 0.10 | –0.56 | –0.17 | –3.75 | <0.001 | ||
| Shortest5000 | –0.71 | 0.10 | –0.91 | –0.50 | –6.99 | <0.001 | ||
| 9 | Weight | 0.65 | 0.06 | 0.52 | 0.77 | 10.52 | <0.001 | 0.910 |
| Longest5000 | –0.36 | 0.08 | –0.51 | –0.20 | –4.62 | <0.001 | ||
| Shortest5000 | –0.69 | 0.08 | –0.85 | –0.54 | –9.01 | <0.001 | ||
| 11 | Weight | 0.56 | 0.07 | 0.43 | 0.69 | 8.53 | <0.001 | 0.881 |
| Longest5000 | –0.38 | 0.09 | –0.56 | –0.19 | –4.17 | <0.001 | ||
| Shortest5000 | –0.82 | 0.09 | –0.99 | –0.64 | –9.50 | <0.001 | ||
| 13 | Weight | 0.25 | 0.11 | 0.03 | 0.48 | 2.29 | 0.027 | 0.690 |
| Longest5000 | –0.66 | 0.15 | –0.96 | –0.37 | –4.53 | <0.001 | ||
| Shortest5000 | –1.11 | 0.14 | –1.39 | –0.83 | –7.95 | <0.001 | ||
| 15 | Weight | 0.19 | 0.10 | –0.02 | 0.40 | 1.80 | 0.078 | 0.715 |
| Longest5000 | –0.80 | 0.13 | –1.07 | –0.54 | –6.04 | <0.001 | ||
| Shortest5000 | –1.21 | 0.14 | –1.49 | –0.92 | –8.58 | <0.001 | ||
| 17 | Weight | 0.23 | 0.11 | 0.01 | 0.44 | 2.11 | 0.040 | 0.714 |
| Longest5000 | –0.77 | 0.13 | –1.04 | –0.51 | –5.86 | <0.001 | ||
| Shortest5000 | –1.15 | 0.15 | –1.45 | –0.85 | –7.83 | <0.001 |
[i] Longest5000: Effective day length of the longest month at 5000 lux.
Shortest5000: Effective day length of the shortest month at 5000 lux.
Table 6
Regression coefficients (standard errors) of predictors for weight (boys).
| Boys | Predictors | Regression coefficient | Standard error | 95% CI Lower | 95% CI Upper | t | p | Adjusted R2 |
|---|---|---|---|---|---|---|---|---|
| Age: 5 | Height | 1.11 | 0.13 | 0.85 | 1.36 | 8.66 | <0.001 | 0.760 |
| Longest5000 | 0.47 | 0.12 | 0.21 | 0.72 | 3.73 | <0.001 | ||
| Shortest5000 | 0.68 | 0.18 | 0.32 | 1.03 | 3.85 | <0.001 | ||
| 7 | Height | 0.89 | 0.13 | 0.63 | 1.14 | 7.09 | <0.001 | 0.762 |
| Longest5000 | 0.51 | 0.12 | 0.26 | 0.76 | 4.13 | <0.001 | ||
| Shortest5000 | 0.43 | 0.17 | 0.09 | 0.78 | 2.51 | 0.016 | ||
| 9 | Height | 1.02 | 0.11 | 0.79 | 1.25 | 8.95 | <0.001 | 0.824 |
| Longest5000 | 0.61 | 0.11 | 0.39 | 0.83 | 5.65 | <0.001 | ||
| Shortest5000 | 0.63 | 0.16 | 0.32 | 0.95 | 4.04 | <0.001 | ||
| 11 | Height | 1.14 | 0.08 | 0.97 | 1.32 | 13.47 | <0.001 | 0.889 |
| Longest5000 | 0.49 | 0.08 | 0.33 | 0.66 | 5.97 | <0.001 | ||
| Shortest5000 | 0.71 | 0.11 | 0.48 | 0.93 | 6.42 | <0.001 | ||
| 13 | Height | 1.21 | 0.10 | 1.00 | 1.41 | 12.12 | <0.001 | 0.874 |
| Longest5000 | 0.63 | 0.09 | 0.45 | 0.81 | 7.08 | <0.001 | ||
| Shortest5000 | 0.89 | 0.13 | 0.63 | 1.15 | 6.90 | <0.001 | ||
| 15 | Height | 0.85 | 0.19 | 0.47 | 1.23 | 4.51 | <0.001 | 0.606 |
| Longest5000 | 0.67 | 0.19 | 0.29 | 1.05 | 3.52 | 0.001 | ||
| Shortest5000 | 0.55 | 0.28 | –0.01 | 1.12 | 1.97 | 0.055 | ||
| 17 | Height | 0.52 | 0.18 | 0.15 | 0.88 | 2.85 | 0.007 | 0.588 |
| Longest5000 | 0.51 | 0.20 | 0.11 | 0.91 | 2.54 | 0.015 | ||
| Shortest5000 | 0.08 | 0.28 | –0.49 | 0.64 | 0.27 | 0.786 |
[i] Longest5000: Effective day length of the longest month at 5000 lux.
Shortest5000: Effective day length of the shortest month at 5000 lux.
Table 7
Regression coefficients (standard errors) of predictors for weight (girls).
| Girls | Predictors | Regression coefficient | Standard error | 95% CI Lower | 95% CI Upper | t | P | Adjusted R2 |
|---|---|---|---|---|---|---|---|---|
| Age: 5 | Height | 1.13 | 0.11 | 0.89 | 1.36 | 9.81 | <0.001 | 0.792 |
| Longest5000 | 0.38 | 0.11 | 0.14 | 0.61 | 3.28 | 0.002 | ||
| Shortest5000 | 0.62 | 0.15 | 0.31 | 0.93 | 4.01 | <0.001 | ||
| 7 | Height | 0.95 | 0.13 | 0.69 | 1.21 | 7.45 | <0.001 | 0.764 |
| Longest5000 | 0.46 | 0.12 | 0.21 | 0.71 | 3.73 | <0.001 | ||
| Shortest5000 | 0.47 | 0.17 | 0.12 | 0.82 | 2.71 | 0.010 | ||
| 9 | Height | 1.10 | 0.10 | 0.89 | 1.31 | 10.52 | <0.001 | 0.847 |
| Longest5000 | 0.50 | 0.10 | 0.31 | 0.70 | 5.17 | <0.001 | ||
| Shortest5000 | 0.67 | 0.14 | 0.39 | 0.94 | 4.92 | <0.001 | ||
| 11 | Height | 1.11 | 0.13 | 0.85 | 1.37 | 8.53 | <0.001 | 0.763 |
| Longest5000 | 0.59 | 0.12 | 0.35 | 0.84 | 4.88 | <0.001 | ||
| Shortest5000 | 0.84 | 0.17 | 0.50 | 1.18 | 4.96 | <0.001 | ||
| 13 | Height | 0.42 | 0.18 | 0.05 | 0.79 | 2.29 | 0.027 | 0.488 |
| Longest5000 | 0.68 | 0.20 | 0.28 | 1.09 | 3.37 | 0.002 | ||
| Shortest5000 | 0.26 | 0.28 | –0.30 | 0.82 | 0.93 | 0.356 | ||
| 15 | Height | 0.37 | 0.20 | –0.04 | 0.78 | 1.80 | 0.078 | 0.440 |
| Longest5000 | 0.46 | 0.24 | –0.02 | 0.95 | 1.92 | 0.062 | ||
| Shortest5000 | 0.00 | 0.32 | –0.65 | 0.65 | 0.00 | 0.999 | ||
| 17 | Height | 0.41 | 0.19 | 0.02 | 0.80 | 2.11 | 0.040 | 0.483 |
| Longest5000 | 0.37 | 0.23 | –0.09 | 0.84 | 1.61 | 0.113 | ||
| Shortest5000 | –0.08 | 0.31 | –0.70 | 0.54 | –0.26 | 0.794 |
[i] Longest5000: Effective day length of the longest month at 5000 lux.
Shortest5000: Effective day length of the shortest month at 5000 lux.
Figure 3
Relationship between effective day length of the longest month and effective day length of the shortest month. The relationship between effective day length of the longest shortest months for each prefecture, in relation to the results of multiple linear regression analysis performed to predict (A) height of 12-year-old boys, (B) weight of 12-year-old boys, (C) height of 17-year-old boys, and (D) weight of 17-year-old boys (Table S5). In relation to multiple regression models (5) and (6), the plot size was determined as the residual of (A) height minus first independent term (H – 0.69W), (B) weight minus first independent term (W – 1.13H), (C) height minus first independent term (H – 0.30W), and (D) weight minus first independent term (W – 0.52H). The gradation of the plot area indicates the sum of the values of the second independent term and the third independent term of multiple regression models (5) and (6), (A) – 0.35 LONG – 0.68 SHORT, (B) – (0.50 LONG + 0.72 SHORT), (C) – 0.72 LONG – 1.10 SHORT, (D) – (0.51 LONG + 0.08 SHORT). As the redness increased, the total effective day length in summer and winter increased.