Lost relation between blood pressure and serum 25-hydroxyvitamin D

BACKGROUND: Low serum 25-hydroxyvitamin D (25(OH)D) levels have consistently been associated with hypertension. During the last decades there has been an unexplained reduction in blood pressure (BP) in Western countries. We therefore examined the relation between serum 25(OH)D and BP in the 7th survey of the Tromsø study 2015/2016. METHODS: Blood pressure and serum 25(OH)D were measured and life-style factors registered in 15,951 subjects not using BP medication. RESULTS: In unadjusted analyses there was a significant negative association between serum 25(OH)D and systolic and diastolic BP that disappeared after adjusting for relevant confounders. This finding is in contrast to our previous reports on 25(OH)D and BP. We therefore cross-sectionally re-analyzed non-smoking (due to interference by smoking in the 25(OH)D assay) subjects not using BP medication from the 4th survey in 1994/1995 (n = 4108), 6th survey in 2007/2008 (n = 7553) and 7th survey 2015/2016 (n = 13,413). Adjusting for age and BMI, there were significant inverse relations between BP and 25(OH)D in the 4th, to a lesser degree in the 6th, and none in the 7th survey. For males the age- and BMI-adjusted differences in systolic BP between those with serum 25(OH)D < 25 nmol/L versus serum 25(OH)D > 100 nmol/L were 6.2 mmHg, 4.1 mmHg and -0.1 mmHg, for the 4th, 6th and 7th surveys, respectively. CONCLUSIONS: Concomitant with a substantial reduction in BP from 1994 to 2015, there has been a loss of relation between 25(OH)D and BP which is hard to explain.