Table 4.

Stepwise linear regression model explaining the variance in s-25(OH)D (nmol/l) dependent on background, seasonal, intake and physical variables based on the food records (n 120); 7-year-old Icelandic girls and boys, Reykjavík, 2006

	Step 1		Step 2		Step 3		Step 4
	β	P value	β	P value	β	P value	β	P value
Background variable
Gender	0·103	0·266	0·06	0·473	−0·008	0·926	−0·074	0·386
Seasonal variable
Week of autumn†			−0·441	<0·001	−0·415	<0·001	−0·389	<0·001
Intake variable
Vitamin D intake (μg/d)					0·251	0·004	0·231	0·006
Physical variables
BMI (kg/m2)							−0·002	0·981
CRF (W/kg per person)‡							0·252	0·005
Adjusted R’2	0·002		0·189				0·241						0·287

s-25(OH)D, serum 25-hydroxyvitamin D; CRF, cardiorespiratory fitness.

†Weeks 36–46.

‡Marker for outdoor activities or sunlight exposure.