Vitamin D is a fat-soluble vitamin and also known as vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Because vitamin D is so important in skeletal growth and strong bones, many foods are fortified with this vitamin to ensure that children obtain adequate amounts.
Ergocalciferol is formed by the action of UV light on plants / yeast.
Cholecalciferol is derived from dietary sources and is also synthesised in your skin via 7-dehydrocholesterol.
Both ergocalciferol and cholecalciferol are inactive until they go through your body and convert via the liver and then the kidneys to the fully active metabolite, calcitriol.
Why you may need vitamin D
Rickets and osteomalacia are both directly related to vitamin D deficiency. Rickets affect children’s bones by causing retarded growth and skeletal abnormalities. The bones become weak and bend to support the body weight causing the most obvious sign of the disease –‘bowed leg’. Osteomalacia occurs in adults where intake of calcium is low and exposure to sunlight is minimal. The bones of the legs soften, become bent and bowed leg. In addition, due to the importance of vitamin D on calcium absorption, osteoporosis can also develop.
Osteoporosis – vitamin D can help prevent / treat osteoporosis. Some research has shown that women with hip fractures have lower levels of plasma vitamin D.
Hypertension – trials have found vitamin D plays a role in regulating blood pressure. It may be linked to the action of vitamin D on calcium. Vitamin D assists the absorption and calcium and helps to maintain proper blood levels of calcium.
How much do you need?
Adequate Intake levels are:
Adults (19-50 years): 5mcg daily
Adults (51-70 years): 10mcg daily
Adults (> 70 years): 15mcg daily
Pregnancy: 5mcg daily
Breastfeeding: 5mcg daily
Children 9-18 years: 5mcg daily
- The National Health and Medical Research Council (NHMRC) of Australia recommend that vitamin D should be obtained by sunlight rather than from dietary sources. Their rationale is that compared to other countries such as England, Australia is sunnier and people tend to spend more time outdoors.
- The NHMRC do recommend that those who are housebound could benefit from an oral intake of 10 mcg (400 IU) vitamin D per day if they are not exposed (face, arms and hands) for 1–2 hours per week to direct sunlight in summer.
Symptoms of deficiency
Vitamin D deficiency leads to inadequate intestinal absorption of calcium and phosphate, osteoporosis, hyperparathyroidism, rickets in children and osteomalacia in adults, tetany (muscle twitching and spasms) and infants may develop convulsions.
The major source of vitamin D is from exposure of the skin to ultraviolet (UV) rays, which results in the synthesis of vitamin D. Best dietary sources include cod liver oil, egg yolks, butter, liver and fortified milk products.
About 15 minutes (depending on your skin pigmentation) of sunlight each day is considered to be equivalent to the ingestion of 5mcg (200 IU) of vitamin D. Choose a time of the day eg early morning or late afternoon when the sun’s rays are not so harsh.
Other reasons why you may need more
There are some factors that increase the demand for vitamin D. These may include pregnancy, breastfeeding, alcohol abuse and malabsorption conditions such as coeliac disease and liver disease.
There is a whole new meaning to location, location, location!! Minimal sun exposure due to location, high pollution, heavy clouds (smog and heavy clouds block the UV rays) can all influence the amount of vitamin D exposure. In addition if you are a strict vegetarian and have little sun exposure or cover up due to cultural reasons you may need to supplement with vitamin D.
Individuals with dark skins (higher melanin concentration) require longer exposure to achieve the same degree of synthesis.
The elderly may have approximately half the capacity for synthesis compared to younger people. Also poor mobility and being housebound can increase the demand for vitamin D.
- Some conditions may be aggravated by vitamin D supplementation. These include hypercalcemia (high calcium in the blood), hyperparathyroidism, sarcoidosis, lymphoma, tuberculosis and kidney stones or kidney disease. Only take vitamin D under the supervision of your medical practitioner.
- Vegetarians – many supplements contain vitamin D3 (cholecalciferol) which is sourced from animal or fish. Vitamin D2 (ergocalciferol) is obtained from plant sources.
- There is no risk of vitamin D toxicity from prolonged exposure to sunlight. Just keep in mind that prolonged exposure to the sun can cause skin cancer and premature wrinkles.
- Excessive dietary intake leads to hypercalcaemia, fatigue, anorexia, diarrhoea, dry mouth and increased thirst, fatigue, headache, nausea vomiting, kidney stones and damage, abnormal heart rhythm and hypertension.