Vitamin D is mainly absorbed through exposure to sunlight, but it can be topped up through eating certain foods and supplements too. Why is vitamin D necessary for maintaining healthy bones? According to Mayo Clinic: “That’s because calcium, the primary component of bone, can only be absorbed by your body when vitamin D is present. Your body makes vitamin D when direct sunlight converts a chemical in your skin into an active form of the vitamin (calciferol).” Prolonged vitamin D deficiency has been linked to a number of health complications – recent evidence links it to a life-long chronic condition.
An epidemiological study conducted by researchers at University of California San Diego School of Medicine and Seoul National University suggests that persons deficient in vitamin D may be at much greater risk of developing diabetes.
The scientists studied a cohort of 903 healthy adults (mean age 74) with no indications of either pre-diabetes or diabetes during clinic visits from 1997 to 1999, and then followed the participants through 2009.
Vitamin D levels in blood were measured during these visits, along with fasting plasma glucose and oral glucose tolerance.
Over the course of time, there were 47 new cases of diabetes and 337 new cases of pre-diabetes, in which blood sugar levels are higher than normal but not yet high enough to be categorised as type 2 diabetes.
The most accurate way to measure how much vitamin D is in a person’s body is the 25-hydroxy vitamin D blood test.
For the study, the researchers identified the minimum healthy level of 25-hydroxyvitamin D in blood plasma to be 30 nanograms per millilitre.
This paper and past research indicate there is a strong association
Cedric F. Garland, study co-author
“We found that participants with blood levels of 25-hydroxyvitamin D that were above 30 ng/ml had one-third of the risk of diabetes and those with levels above 50 ng/ml had one-fifth of the risk of developing diabetes,” said first author Sue K. Park, MD, in the Department of Preventive Medicine at Seoul National University College of Medicine in South Korea.
Study co-author Cedric F. Garland, DrPH, adjunct professor in the UC San Diego School of Medicine Department of Family Medicine and Public Health, said persons with 25-hydroxyvitamin D levels below 30 ng/ml were considered vitamin D deficient.
These persons, the researchers found, were up to five times at greater risk for developing diabetes than people with levels above 50 ng/ml.
Garland, who has previously investigated connections between vitamin D levels and various types of cancer, said the study builds upon previous epidemiological research linking vitamin D deficiency to a higher risk of diabetes.
Epidemiological studies analyse the distribution and determinants of health and disease conditions. They do not necessarily prove cause-and-effect.
“Further research is needed on whether high 25-hydroxyvitamin D levels might prevent type 2 diabetes or the transition from pre-diabetes to diabetes,” said Garland. “But this paper and past research indicate there is a strong association.”
To reach 25-hydroxyvitamin D levels of 30 ng/ml, Garland said would require dietary supplements of 3,000 to 5,000 international units (IU) per day, less with the addition of moderate daily sun exposure with minimal clothing (approximately 10-15 minutes per day outdoors at noon).
“From about late March/early April to the end of September, most people should be able to get all the vitamin D they need from sunlight,” explained the NHS.
But certain people are at a greater risk of vitamin D deficiency, such as people that aren’t often outdoors.
A diet rich in vitamin D may help to compensate for the lack of sunlight exposure.
As the NHS outlined, rich sources of the vitamin include:
- Oily fish – such as salmon, sardines, herring and mackerel
- Red meat
- Egg yolks
- Fortified foods – such as most fat spreads and some breakfast cereals
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