There are 'clear indications' that heart disease may be caused by vitamin D deficiency, say researchers from the University of Bonn in Germany, who, in co-operation with the Bad Oeynhausen Heart Centre, have been studying the causes of cardiac failure.
In a group of patients with chronic heart failure, vitamin D blood levels were up to 50 per cent lower than in a control group, report the scientists in the Journal of the American College of Cardiology. They also found a correlation between disease severity and vitamin D levels.
Around 15 million people worldwide suffer from heart failure, and yet every second patient - whether they are young or old - dies within the first five years after the disease has been diagnosed, noted the researchers.
The team from Bonn explained that in heart failure the vena cava muscle is weakened to such an extent that the heart can no longer pump sufficient quantities of blood through the body. The poor circulation means the kidneys cease to function properly and can no longer dehydrate the body adequately. This leads to hydropexis in the tissues, known as edemas. The heart reacts by releasing the hormone ANP, which promotes fluid elimination. A high blood level of ANP is thus a reliable indicator of cardiac failure, claim the researchers, even in early stages when the disease hardly shows any symptoms.
They add that it has long been recognised that vitamin D in cell cultures slows down the production of the 'dehydration' hormone ANP. Chicks with vitamin D deficiency develop heart failure, which disappears again as soon as the vitamin is added to their feed. And in the cardiac muscle cells of rats scientists have been able to detect a large number of receptors for vitamin D. Therefore they assumed that the substance found in eels, salmon and herring might also be relevant for human chronic heart failure (CHF) symptoms.
Dr Armin Zittermann and a PhD student of the Bonn Institute of Nutrition studied 54 heart failure patients and 34 healthy people as a control group, in what they claim is the first study of its kind worldwide. They determined the concentration of two different vitamin D metabolites in the blood of the study participants: in patients with CHF, vitamin D blood levels were up to 50 per cent lower than in the control group. The ANP level, by contrast, had increased to more than twice the normal level in the CHF patients. There was a correlation between the degree of disease severity and the extent of the vitamin D deficiency.
"All these data are clear indications that an insufficent supply of vitamin D can be important in the emergence of chronic heart failure," Dr Zittermann said. The two researchers are currently carrying out a follow-up study in which they give the CHF patients vitamin D and check whether their condition improves.
The scientists added that vitamin D plays an important role in regulating the calcium concentration in the body - for example, by improving the absorption of calcium from the intestine. However, it also appears to be able to influence the calcium 'transfer' in the cardiac cells. So that the muscle can contract, the calcium concentration has to be briefly boosted. For this purpose, the heart taps into a calcium reserve within the cell which it then fills up again by means of little 'pumps' during the relaxation phase. Vitamin D seems to influence the activity of these mini-pumps. However, if they do not work properly, the myocardium cannot contract completely.
Between 75 to 90 per cent of vitamin D made by people is derived from UVB irradiation in the skin. The rest is absorbed via our food. This is why people who are stuck behind their desks in an office do not produce enough vitamin D, and in the winter months the intensity of UVB irradiation is insufficient in many countries.
"In industrial countries vitamin D deficiency is a common phenomenon," explained Dr Zittermann. And as people get older, they lose the ability to synthesise this valuable substance themselves - an 80-year-old only produces a quarter of the amount a 20-year-old does from the same UVB irradiation. "Interestingly, almost all senior citizens suffer from at least moderate CHF," he said.
However, the authors cautioned that at present the possibility cannot be excluded that heart disease itself contributes to low vitamin D levels, thereby producing a vicious circle - patients with heart disease, after all, are only rarely exposed to the sun due to their few outdoor activities.
And the scientists did not advise stepping up sunbathing activities. "UV radiation is simply too dangerous for that," Dr Zittermann explained. "Apart from that, the link between low vitamin D status and heart failure still needs to be conclusively proved."
Regular intake of food rich in vitamin D would certainly do no harm, however, although the substance is only present in substantial amounts in fish, so they recommend two to three meals a week involving fish.