Low vitamin D level may lead to high blood pressure

1 August, 2007:

As the level of vitamin D in the blood drops, blood pressure increases, a health survey has found.

The analysis from the survey – conducted between 1988 and 1994 – involved 12,644 adults in America aged 20 years and above, who had blood pressure recorded and vitamin D levels measured.

The results of the survey, reported in the July 2007 issue of American Journal of Hypertension, found that people with the lowest vitamin D levels had blood pressure that was slightly higher than those with the highest levels. This relationship was strongest in subjects who were 50 years of age and above.

The authors of the study noted that “vitamin D levels can easily, and cheaply, be increased by a modest increase in sun exposure or vitamin D supplementation,” but cautioned that “first it needs to be confirmed by large, well-designed intervention studies.”

Dr Robert Scragg and colleagues from the University of Auckland, the University of Michigan, and the Hunter New England Area Health Service (Australia) found that those who had low levels of vitamin D in their blood had slightly higher blood pressure compared to those who had higher levels of vitamin D.

Vitamin D generally refers to two entities – cholecalciferol (D3) and ergocalciferol (D2). D3 is produced in the body following exposure to UVB radiation in the range of 290 to 320 nm, while D2 is obtained from dietary sources, including oily fish such as salmon, sardines, and mackerel as well as cod liver oil, milk, cereal, and orange juice.

Deficiency of vitamin D has been linked to many conditions, including metabolic syndrome.

The researchers aimed at examining whether there was any association between serum 25-hydroxyvitamin D (25OHD), the non-active ‘storage’ form of both D3 and D2, and blood pressure in certain ethnic groups in an effect to explain why African-Americans in the United States and the United Kingdom have increased blood pressure compared to whites.

For the study, they analysed data from the Third US National Health and Nutrition Examination Survey (NHANES III), which involved 12,644 people aged 20 and above with their 25- hydroxyvitamin D status and blood pressure measured. None of subjects were on medications indicated for treatment of hypertension.

Non-Hispanic whites had the highest blood levels of vitamin D, followed by Mexican Americans. Non-Hispanic African-Americans had the lowest blood levels of vitamin D.

It is commonly believed that African-Americanshave low levels of vitamin D since they cannot absorb ultraviolet rays well from sunlight because of their skin pigments.

The researchers found that systolic blood pressure in people with high levels of vitamin D was at least 3.0 mm of Hg lower than those with low vitamin D levels. Similarly, diastolic blood pressure was 1.6 mm of Hg lower in those with high levels of vitamin D than those with low levels.

The results were obtained after age, sex, ethnicity, and physical activity were considered.

The inverse association between vitamin D and blood pressure was weakened after body mass index was considered, but was still significant for systolic blood pressure. The association was more significant in people aged 50 or above than younger people.

Early in 2004, the same team of researchers had analysed data from the same study and found that low vitamin D was linked to increased risk of diabetes among non-Hispanic whites and Mexican Americans, but not in non-Hispanic African-Americans.

The current study is a statistic analysis, which could not reveal any causal relationship between vitamin D and blood pressure – meaning that taking vitamin D supplements or eating foods rich in the vitamin or high exposure to sun rays may or may not improve blood pressure.