Calcium, Vitamin D and Bone Health and Dexa Scan

Osteoporosis is a condition in which the skeleton loses bone mass and minerals, and bones become more porous, thinner and weaker, leading to an increased risk of a fracture. Osteoporosis is on the increase in Ireland, partly due to the ageing population, but also to dietary and lifestyle influences. People usually equate osteoporosis with a poor intake of calcium, the menopause in women and older age. This is certainly true – but excess alcohol, protein malnutrition, smoking, some medications, lack of exercise and other lifestyle factors also impair bone health. We will arrange a Dexa Scan as needed through our local hospital systems.


Calcium is a vital bone-building material – protecting against osteoporosis – but it cannot do its job without adequate vitamin D. Bone also provides the “calcium reservoir” for maintaining correct calcium levels in the blood. Milk and dairy foods are among the richest and most easily accessible sources of calcium – a 250ml glass of milk contains about 300mg calcium. Three servings of dairy foods a day usually ensures adequate calcium intake of around 1000mg per day. Other good sources are foods and beverages fortified with calcium, small fish with bones, nuts, tofu and certain vegetables (eg, broccoli).

In one vulnerable group – teenage girls – calcium intake fell well short of the recommended 1000mg, a recent Irish study showed. Many adults also did not consume two to three dairy servings a day and were probably not meeting the recommended intakes. Bone density and strength can be compromised later in life if there is inadequate calcium consumption, particularly during the growing years and early adulthood.

Vitamin D

Vitamin D occurs naturally in small amounts in some foods (see below) but diet is not the main source – vitamin D is mainly created through the action of sunlight on the skin. Most diets (without supplements) are not thought to provide sufficient vitamin D. An international study of over 2500 postmenopausal women who have osteoporosis has found most of these women are deficient in vitamin D. Vitamin D was first identified as being an essential nutrient when it was discovered children given cod liver oil (high in vitamin D) did not develop rickets (early age bone deformities). Later, it was found that exposure to sunlight had a similar effect (see below). And, even recently, an Irish study has reported that, while figures are no longer routinely kept, cases of rickets in children are still appearing. A vitamin D deficiency during pregnancy is believed to be an important cause (the infant also starts life with a deficiency), as is extreme protection of children from sunlight.

Vitamin D and calcium should be considered of equal importance for maintaining healthy bones throughout your entire life. Vitamin D has many functions but bone health is an important one.

  • Vitamin D allows calcium absorption; without it your digestive system cannot absorb as much calcium from food.
  • Vitamin D is needed for the proper mineralisation and growth of bone.
  • Studies have shown that correction of vitamin D and calcium deficiencies in elderly women reduces fracture rates.
  • Correction of vitamin D deficiency separately reduces body sway and the risk of falling in elderly women, perhaps by improving nerve-muscle function.
  • Evidence increasing points to a role for vitamin D in the immune system and regulating blood pressure.

Foods containing vitamin D

  • Fatty fish, eg, salmon, mackerel, sardines (rich source)
  • Cod liver oil (rich source)
  • Liver
  • Some fortified foods (moderate source), eg:
    -dairy foods

Vitamin D: the “sunshine” vitamin

Vitamin D is often referred to as the sunshine vitamin – normally, 90% of our requirement comes from the action of sunlight (ultraviolet light; UV), which penetrates the skin and activates pre-vitamin D into vitamin D (through reactions in the skin, liver and kidneys). Vitamin D manufacture by the skin is normally much greater than the amounts obtained from food. Exactly how much vitamin D is obtained from the ultraviolet light in sunlight, and therefore how much sun exposure is needed each day, depends on:

  • Skin pigmentation – darker skin needs more UV to produce vitamin D
  • Season, time of day – the less intense the sun, the more is needed
  • Duration of exposure to sunlight
  • Coverage by clothing or sunscreen
  • Whether sitting behind glass or plastic.

Consequently, those at risk for a vitamin D deficiency include:

  • Darker skinned adults
  • Dark-skinned children, particularly if they are also iron deficient
  • People whose skin is largely always covered for religious reasons or custom (especially women and children)
  • Vitamin D deficient pregnant women who may predispose newborns to vitamin D deficiency
  • Infants entirely breastfed beyond six months without sunlight exposure or vitamin D supplementation
  • Older adults who are seldom outside (eg, housebound or in residential care) and are not receiving vitamin D supplementation.

How much sun exposure is needed?

If the adequate sun exposure is not possible a daily vitamin D supplement of 400IU (10 micrograms) is recommended. Dark-skinned people will require more sun exposure than fair skinned people. Ultraviolet light is the radiation most commonly associated with sunburn and skin cancer.

Comments in medical journals in 2010 describe frank vitamin D deficiency in up to 8% of younger women at the end of winter and in 15% of dark-skinned pregnant women attending an antenatal clinic in Dublin. A similar proportion (17%) with deficiency was found in a study of 90 pregnant women of all backgrounds and ethnicities attending an antenatal health service check. Other researchers in Dublin found up to 46% of elderly people in nursing homes had very low levels of vitamin D. The elderly are most at risk of developing osteoporosis and having falls and fractures if adequate calcium and vitamin D are not maintained. Doctors are well aware of the osteoporosis risks and can help you identify whether you are at risk of a nutritional deficiency or developing osteoporosis. If you have a deficiency, supplementation of calcium and vitamin D may be recommended.