In recent years evidence has been amassing which has linked vitamin D with protection from a variety of ills including osteoporosis, multiple sclerosis, low mood and several forms of cancer. Recently, US-based researchers have produced research which suggests that this nutrient has the capacity to ward off high blood pressure (hypertension too).

A part of this research, about 600 men and 1200 women who had their blood vitamin D levels measured were then assessed for a period of 4-8 years. In men, those with vitamin D levels less than 15 ng/ml (evidence of vitamin D deficiency) were found to be 6 times more likely to suffer from hypertension compared to men with vitamin D levels of 30 ng/ml or above. In women, vitamin D levels of less than 15 ng/ml were found to be associated with twice the risk of hypertension compared to those with levels of 30 ng/ml or more.

This sort of ‘epidemiological’ study may show an association between higher levels of vitamin D and lower blood pressure, but cannot prove that vitamin D is actually causing this effect. However, as the researchers involved in this study point out, vitamin D has known actions in the body that would be expected to help reduce blood pressure.

For example, laboratory studies have found that vitamin D suppresses the activity of the hormone ‘renin’ – high levels of which can cause raised blood pressure. Vitamin D also has the capacity to reduce the proliferation of muscle in the walls of blood vessels, something that would also be expected to help protect against blood vessels ‘stiffness’ and high blood pressure.

The signs are that vitamin D does have a genuine blood-pressure lowering effects. If this is the case, then this should help explain why individuals living the ‘Mediterranean’ region are found to have a generally reduced risk of heart disease. While the ‘Mediterranean’ diet has been much used to explain this phenomenon, perhaps sunlight is playing a yet unsung role here too.

Indeed, in one study undertaken in Turkish children, blood pressure was found to be significantly lower in the summer than the winter. What is more, the researchers of this study found by measuring the concentration of the children’s urine that this difference could not be explained by variation in level of hydration in the children.

Most of the body’s needs of vitamin D are met by the action of sunlight on the skin. During the darker months, lower light exposure can lead to reduced vitamin D levels, which it seems may have important consequences for health. In a previous blog, I wrote about how cod liver oil may be used to help prevent vitamin D deficiency during the winter [3]. Another tactic, of course, is just to get out more.

References:

1. Forman JP, et al. Plasma 25-Hydroxyvitamin D Levels and Risk of Incident Hypertension.
Hypertension. 2007 Mar 19;[Epub ahead of print]

2. Polat M, et al. The effect of seasonal changes on blood pressure and urine specific gravity in children living in Mediterranean climate. Med Sci Monit 2006 Apr;12(4):CR186-90. Epub 2006 Mar 28

3. How vitamin D deficiency in winter poses hazards for our health (and what to do about it)

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