Seasonal variations of insulin sensitivity from a euglycemic insulin clamp in elderly men

Figures & data

Table I. Clinical characteristics of study participants presented for winter and summer seasons and coefficients of variation determined by the reliability study performed.

Variable	Winter season	Summer season	P ^b	CV (%)
Temperature (°C)	3.1 (4.4)	10.9 (3.2)	–
M/I (100 × mg × min^-1 × kg^-1/(mU × L^-1))	4.84 (2.44)	5.44 (2.53)	0.0003	13.9
HOMA-IR (pmol × mmol/L^2)	77.0 (56.0)	81.0 (72.7)	0.11	15.6
Incremental area under insulin curve (pmol × min/L)	1167 783	1003 (632)	0.007	42.6
Fasting plasma glucose (mmol/L)	5.80 (1.52)	5.71 (1.32)	0.28	5.8
2-h plasma glucose (OGTT) (mmol/L)	8.35 (4.03)	8.27 (4.09)	0.58	14.2
Energy intake (kcal)^a	1735 456	1772 (467)	0.22
Height (cm)	174.8 (5.8)	174.7 (6.4)	0.88	0.0
Weight (kg)	80.7 (11.4)	79.6 (11.9)	0.18	0.8
BMI (kg/m^2)	26.4 (3.4)	26.0 (3.4)	0.12	0.8
Waist circumference (cm)	95.0 (9.5)	93.7 (9.7)	0.03	2.3
25-Hydroxyvitamin D (nmol/L)	66.5 (17.8)	72.5 (20.7)	< 0.0001
Smoker (%)	20.5	20.9	0.88
High usual leisure time physical activity (%)	60.0	63.9	0.23
Type 2 diabetes (%)	14.3	16.0	0.52
Impaired glucose tolerance (%)	13.1	12.1	0.67
Diabetes medicine: per oral (%)	5.3	3.4	0.15
Hypertension medicine: ACE inhibitors (%)	6.1	6.1	0.99
Hypertension medicine: beta blockers (%)	19.6	17.2	0.33

Data presented are: Mean (SD) or % for winter season (October–April), n = 810; and summer season (May–September), n = 307. Coefficients of variation (CV) from the reliability study, n = 20.

^aData on energy intake is presented from a subset (winter season, n = 762; summer season, n = 288).

^bAdjusted for age.

Figure 1. Mean values of insulin sensitivity index M/I (solid line) (100 × mg × min^-1 × kg^-1/(mU × L^-1)) from a euglycemic insulin clamp, and outdoor temperature (dotted line) (degrees Celsius), versus winter (W) and summer (S) seasons of the year from the years 1991 to 1995. Outdoor temperature is the mean of observed outdoor temperatures of the month of the investigation and the 2 months preceding it.