According to findings published in Diabetes Care, a study with 3,262 Chinese people aged between 50 and 70 showed that 94 per cent were vitamin D deficient or insufficient, and 42 per cent of these people also had metabolic syndrome.
“Vitamin D deficiency is becoming a condition that is causing a large burden of disease across the globe with particular deleterious impact among the elderly,” said researcher Dr Oscar Franco from Warwick Medical School in England.
While the study was conducted in elderly Chinese people, Dr Franco said the results are consistent with the findings of other studies in Western populations, and he suggested vitamin D deficiency could become a global health problem.
In adults, it is said vitamin D deficiency may precipitate or exacerbate osteopenia, osteoporosis, muscle weakness, fractures, common cancers, autoimmune diseases, infectious diseases and cardiovascular diseases. There is also some evidence that the vitamin may reduce the incidence of several types of cancer and type-1 diabetes.
“Our results are consistent with those found in British and American populations. We found that low vitamin D levels were associated with an increased risk of having metabolic syndrome, and was also significantly associated with increased insulin resistance,” he said.
Metabolic syndrome (MetS) is a condition characterised by central obesity, hypertension, and disturbed glucose and insulin metabolism. The syndrome has been linked to increased risks of both type-2 diabetes and cardiovascular disease (CVD).
In collaboration with colleagues from the Shanghai Institute of Biological Sciences in China, the researchers analysed Vitamin D levels in participants of the Nutrition and Health of Aging Population in China (NHAPC) project. Vitamin D levels were calculated using serum concentrations of 25-hydroxyvitamin D (25(OH)D), the non-active 'storage' form of the vitamin in the body.
Vitamin D insufficiency, quantified as 25(OH)D levels below 75 nmol/L, was documented in 24 per cent of the people studied. Vitamin D deficiency, defined by the authors as 25(OH)D levels below 50 nmol/L, was recorded in 69 per cent of the people.
People with the lowest average 25(OH)D levels (28.7 nmol/l) were 52 per cent more likely to have metabolic syndrome than people with the highest average 25(OH)D levels (57.7 nmol/l), noted Franco and his co-workers.
Furthermore, the researchers noted links between 25(OH)D levels and insulin levels and insulin resistance in overweight and obese, but not normal weight, individuals.
“Vitamin D deficiency is common in the middle-aged and elderly Chinese and low 25(OH)D level is significantly associated with increased risk of having MetS and insulin resistance,” wrote the authors in the journal.
"Vitamin D deficiency is now recognised as a worldwide concern and metabolic syndrome has become a global epidemic. More research is needed to find out why older people are more likely to have lower levels of vitamin D and how this is linked to the development of metabolic syndrome and related metabolic diseases," said Dr Franco.
Sun, fish or supplements?
The study adds to an ever growing body of science supporting the benefits of maintaining healthy vitamin D levels.
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.
While our bodies do manufacture vitamin D on exposure to sunshine, the levels in some northern countries are so weak during the winter months that our body makes no vitamin D at all, meaning that dietary supplements and fortified foods are seen by many as the best way to boost intakes of vitamin D.
Commenting independently on the study, Ed Yong from British charity Cancer Research UK said: "The amount of sunlight it takes to make enough vitamin D is always less than the amounts that cause reddening or burning, so it should be possible to get the benefits of this vitamin without increasing the risk of skin cancer.
"Elderly people can also boost their vitamin D levels by eating foods like oily fish, or by using vitamin D supplements on the advice of their GP."
Source: Diabetes Care Published online ahead of print, doi: 10.2337/dc09-0209“Plasma 25-hydroxyvitamin D Concentration and Metabolic Syndrome among Middle-aged and Elderly Chinese” Authors: L. Lu, A. Pan, F.B. Hu, O.H. Franco, H. Li, X. Li, X. Yang, Y. Chen, Z. Yu, X. Lin