Vitamin D plays three key roles in bone health:
- Helps with calcium absorption from food in the intestine
- Ensures the correct renewal and mineralization of bone
- Helps to keep muscles strong and so reduces the risk of falling
Vitamin D is made in the skin when the skin is exposed to UV-B rays in sunlight. Only a limited number of foods contain vitamin D, so exposing the skin to sunlight is how we get 70-80% of the vitamin D our body needs.
The type of vitamin D made in the skin is called vitamin D3 (cholecalciferol) and the form of vitamin D that you get through your diet is either vitamin D3 or a closely related molecule of plant origin known as vitamin D2 (ergocalciferol).
How much sun exposure do you need?
To get enough vitamin D, generally, you should try to get 10–20 minutes of sun exposure to your bare skin (face, hands, and arms) outside peak sunlight hours (before 10 AM and after 2 PM) daily – without sunscreen – and taking care not to burn.
Unfortunately, sunlight is not always a reliable source of vitamin D. The season and geographic latitude, use of sunscreen, city smog, skin pigmentation, and a person’s age are just some of the factors that will affect how much vitamin D is produced in the skin through sunlight.
Because many of us spend most of our times indoors, low levels of vitamin D have become a worldwide problem and there is concern that this is having a negative impact on bone health.
Sources of Vitamin D in foods
Very few foods are naturally rich in vitamin D. As a result, in some countries, certain food and drinks such as margarine, breakfast cereals, and orange juice are fortified with vitamin D. Natural food sources of vitamin D include oily fish (such as salmon, sardines and mackerel), eggs, mushrooms and liver.
Vitamin D content (IU) *
Shitake mushrooms, fresh
Shitake mushrooms, sun-dried
20 per yolk
*per 100 mg unless otherwise stated
IU: International Unit
Recommended vitamin D intake
There is no common definition of ‘optimum’ vitamin D intake and that’s one reason why dietary recommendations for vitamin D are approximate. Many countries recommend a dietary intake of 200 IU/day (5 µg/day) for children and young adults, and 400-600 IU/day (10-15 µg/day) for older persons, to boost the amount of vitamin D that is made in the skin from sun exposure.
It is very common for seniors to have low vitamin D levels. This is because they tend to stay indoors or avoid sunshine. Also, in the elderly, the skin produces less vitamin D when exposed to the sun as compared to younger people.
As a result, IOF recommends that seniors aged 60 years and over take a supplement at a dose of 800 to 1000 IU/day to benefit bone health and help reduce the risk of falls.
For people with osteoporosis, combined calcium and vitamin D supplements are recommended to ensure that they are getting enough of these important nutrients and to maximize the benefits of osteoporosis treatment.
Vitamin D deficiency
In children, severe vitamin D deficiency can lead to bone deformities known as rickets. In adults, the same condition is known as osteomalacia. In industrialised countries, rickets and osteomalacia are relatively rare. However, low levels of vitamin D are common, affecting bone health and osteoporosis risk. Having enough vitamin D during pregnancy is important too because there is some evidence that a deficiency during pregnancy can lead to children with reduced bone mass, which could, in turn, be a risk factor for osteoporosis later in life.