This underrated vitamin is found in certain foods but is also produced by the body in response to exposure to the sun.
When the sun’s ultraviolet-B (UVB) rays are exposed to bare skin, the body converts a cholesterol derivative into vitamin D. In fact, it’s now known that every cell and tissue within the body has a vitamin D protein receptor.
However, many people in the UK and other Western countries are deficient in vitamin D, including many people with type 2 diabetes, due to limited sunlight exposure caused by a number of factors, including more time spent at homen, in the office or the car, shorter days in winter, sunscreen use in summer, age and skin colour.
According to the NHS, humans do not make enough vitamin D from sunlight between October and early March, which may explain why people can become vitamin D deficient.
Which foods contain vitamin D?
Vitamin D is only found in a few foods. These include:
- Red meat
- Oily fish
- Vitamin D fortified foods
You can also take supplements. Single vitamin D supplements or vitamin drops containing vitamin D (for use by young children) are available at most UK pharmacies, supermarkets and health food retailers like Holland and Barrett.
How much vitamin D am I supposed to have?
Adults and children from the age of 1 year onwards require 10μg (micograms) of vitamin D daily as per the NHS recommendations.
10μg is equivalent to 400 IU, the International Unit equivalent. A milligram (mg) is 1000 times bigger than a microgram.
In the USA, children and adults under 71 years old are advised to have 600 IU of vitamin D a day.
Most multivitamins provide a daily dosage of 400 International Units (IU).
Be careful not to take too much vitamin D, as persistent high intake of vitamin D can lead to hypercalcaemia, a condition where calcium builds up in the body.
How much sunshine do I need for enough vitamin D?
How much sunshine you need to produce enough vitamin D is a common question.
Unfortunately, there is no straight answer. The daily dose of sunshine required is affected by a number of factors including how much sunscreen you are wearing, your skin colour, how much of your body is exposed, and your latitude.
It has been estimated that Caucasians would need 9 minutes of sun at lunchtime daily to remain non-vitamin D deficient. This assumes summer wear (think shorts and a t shirt) from June to August, while only having their hands and faces exposed from March to June and for September.
It was estimated that people of South Asian origin would require 25 minutes.
What should my vitamin D levels be?
Vitamin D levels should ideally be between 20-50 ng/ml (50-125 nmol/l)*, with anything below 30 ng/ml considered deficient.
*Note; the correct level of vitamin D varies from person to person. The only way to be sure that your vitamin D levels are where they should be is to request a 25-hydroxyvitamin D, or 25(OH)D, blood test from your GP or do a vitamin D test at home.
Vitamin D deficiency
The signs of vitamin D deficiency can range from bone pain and muscle weakness to depression and weakened immune system, while longer-term deficiency can result in obesity, high blood pressure, psoriasis, osteoporosis, chronic fatigue, Alzheimer’s disease, cancer and type 2 diabetes
Effects on diabetes
Vitamin D is believed to help improve the body’s sensitivity to insulin – the hormone responsible for regulating blood sugar levels – and thus reduce the risk of insulin resistance, which is often a precursor to type 2 diabetes.
Some scientists also believe this vitamin may help regulate the production of insulin in the pancreas.
Other health benefits
As well as assisting glycemic control, increasing your levels of vitamin D can also:
- Aid weight loss – studies have shown that good vitamin D status helps to reduce parathyroid hormone (PTH) levels, which in the long-term may promote weight loss and reduce risk of obesity, which is a major risk factor for type 2 diabetes.
- Regulate appetite – vitamin D can increase your body’s levels of the hormone leptin, which controls body fat storage and triggers the sensation of satiety, giving the feeling of having eaten enough and thus lowering hunger levels.
- Reduce belly fat – an increase in vitamin D can help lower levels of cortisol, a stress hormone produced in the adrenal glands. Cortisol is involved in a number of important functions, including the body’s response to stress and regulation of blood pressure. But higher and more prolonged levels of the hormone in the blood can lead to increased abdominal (or visceral ) fat, which is linked to various health conditions including diabetes type 2.
Types of vitamin D
There are two forms of this vitamin; vitamin D2 and vitamin D3
Vitamin D2 is a synthetic version called ergocalciferol, which has a shorter shelf life, while vitamin D3 (also known as cholecalciferol) is the same as the vitamin D that is produced by the body following exposure to UVB rays.
Studies have shown that vitamin D3 appears to be more than three times as effective as vitamin D2, but most products that include the words “good source of vitamin D” or “fortified with vitamin D” on their labels contain the hugely inferior vitamin D2.
So when shopping for vitamin D-rich foods or supplements, make sure you check which ‘type’ of vitamin D each product contains.
 NHS: Vitamin D.
 National Institute of Health: Vitamin D
 Webb AR, Kazantzidis A, Kift RC, Farrar MD, Wilkinson J, Rhodes LE. Meeting Vitamin D Requirements in White Caucasians at UK Latitudes: Providing a Choice. Nutrients. 2018 Apr 17;10(4):497. doi: 10.3390/nu10040497. PMID: 29673142; PMCID: PMC5946282.
 Webb AR, Kazantzidis A, Kift RC, Farrar MD, Wilkinson J, Rhodes LE. Colour Counts: Sunlight and Skin Type as Drivers of Vitamin D Deficiency at UK Latitudes. Nutrients. 2018 Apr 7;10(4):457. doi: 10.3390/nu10040457. PMID: 29642423; PMCID: PMC5946242.