[PHNUTR-L] Low vitamin D levels linked to higher blood pressure

[Kathrynne Holden]

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Low vitamin D levels linked to higher blood pressure

By Stephen Daniells
http://www.nutraingredients.com/news/ng.asp?n=78482&m=2nie727&c=xeiqgoegavfxtla

25/07/2007 - People with low blood levels of vitamin D may be at an 
increased risk of higher blood pressure - a problem that could be easily 
remedied with supplements, says a new study.

"This finding may have public health significance, as vitamin D levels 
can easily, and cheaply, be increased by a modest increase in sun 
exposure or vitamin D supplementation," wrote lead author Robert Scragg 
in the American Journal of Hypertension.

"However, first it needs to be confirmed by large, well-designed 
intervention studies," he cautioned.

In the UK alone, there are an estimated 10m people with hypertension, 
defined as having blood pressure higher than 140/90 mmHg. The condition 
is a major risk factor for cardiovascular disease (CVD), which causes 
almost 50 per cent of deaths in Europe, and is reported to cost the EU 
economy an estimated €169bn ($202bn) per year.

The researchers, from the University of Auckland, University of 
Michigan, Hunter New England Area Health Service (Australia), used data 
from Third US National Health and Nutrition Examination Survey (NHANES 
III). The analysis was confined to 12,644 people (aged 20 or over, 6547 
women) and those on hypertensive medication were excluded.

Vitamin D status was measured using blood levels of 25- hydroxyvitamin D 
(25(OH)D).

Vitamin D refers to two biologically inactive precursors - D3, also 
known as cholecalciferol, and D2, also known as ergocalciferol. The 
former, produced in the skin on exposure to UVB radiation (290 to 320 
nm), is said to be more bioactive. The latter is derived from plants and 
only enters the body via the diet, from consumption of foods such as 
oily fish, egg yolk and liver.

Both D3 and D2 precursors are hydroxylated in the liver and kidneys to 
form 25- hydroxyvitamin D (25(OH)D), the non-active 'storage' form, and 
1,25-dihydroxyvitamin D (1,25(OH)2D), the biologically active form that 
is tightly controlled by the body.

The researchers report that non-Hispanic whites had the highest blood 
levels, followed by Mexican Americans, while non-Hispanic blacks had the 
lowest vitamin D levels.

"Age- and gender-adjusted mean blood pressures were higher in 
non-Hispanic blacks than in Mexican Americans and non-Hispanic whites, 
consistent with results from the first phase (1988 to 1991) of NHANES 
III," stated the researchers.

"The finding that ethnic differences in vitamin D status explained about 
half of the increased prevalence of hypertension in non-Hispanic blacks, 
compared with non-Hispanic whites, supports the previous suggestion that 
low vitamin D levels in non-Hispanic blacks may be a factor in their 
increased hypertension prevalence," they added.

When the subjects were split up into five groups depending on blood 
levels, the researchers calculated that people with the highest average 
25(OH)D levels (at least 85.7 nmol/L) had systolic diastolic and blood 
pressure 3.0 and 1.6 mm Hg lower, respectively, than people with the 
lowest levels (40.4 nmol/L or less).

After adjusting the results to account for BMI the associations remained 
statistically significant for systolic blood pressure.

"These results from a nationally representative US sample show that 
systolic BP and pulse pressure are inversely associated with serum 
25OHD... The inverse association between serum 25OHD and systolic BP has 
clinical significance, because the latter variable is a better predictor 
of coronary heart disease risk than diastolic BP, particularly in older 
people," wrote the researchers.

Calls to increase vitamin D intake have been growing. Indeed, only 
recently fifteen experts from universities, research institutes, and 
university hospitals around the world called for international agencies 
to "reassess as a matter of high priority" dietary recommendations for 
vitamin D because current advice is outdated and puts the public at risk 
of deficiency (The American Journal of Clinical Nutrition, Vol. 85, pp. 
860-868).

A recent review of the science reported that the tolerable upper intake 
level for oral vitamin D3 should be increased five-fold, from the 
current tolerable upper intake level (UL) in Europe and the US of 2000 
International Units (IU), equivalent to 50 micrograms per day, to 10,000 
IU (250 micrograms per day).

Source: American Journal of Hypertension (Elsevier)
July 2007, Volume 20, Issue 7, Pages 713-719
"Serum 25-hydroxyvitamin D, Ethnicity, and Blood Pressure in the Third 
National Health and Nutrition Examination Survey "
Authors: R. Scragg, M. Sowers and C. Bell
-- 
Kathrynne Holden, MS, RD < fivestar at nutritionucanlivewith.com >
"Ask the Parkinson Dietitian"  http://www.parkinson.org/
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