With the evenings getting shorter this time of year, we are generallly exposed less to sunlight. This has a number of effects on our bodies, one of which is a lessening of production of Vitamin D. Parents of newborn infants will also be aware of the emphasis on Vitamin D supplement drops for their new arrivals. So this week we’ll take a look at this vitamin.
Vitamin D differs from the other vitamins in that the body can make it on its own without having to ingest it from external sources. It is synthesised from cholesterol in the skin when exposed to ultraviolet light. Alternatively, it can be ingested as cholecalciferol (D2) or ergocalciferol (D3). All these forms of Vitamin D are inactive on the body. They are initially converted in the liver to Calcidiol which is in turn converted in the kidneys to Calcitriol. Calcitriol is the active form of vitamin D and is transported to the target organs around the body.
Vitamin D has numerous functions in the body including modulating cell growth and helping to regulate the immune system. It’s most important function, however, is probably in promoting calcium absorption in the gut. It also maintains adequate calcium and phosphate concentrations to enable minerlisation of the bones. With insufficient levels of Vitamin D, the bones become brittle and misshapen. In children this can lead to a condition known as Rickets, where the bones soften and can fracture. This had all but disappeared from modern society for a number of years, but doctors are reporting a return of the condition in children due to poor diet, low intake levels of foods fortified with Vitamin D, and lack of exposure to sunlight. In the elderly, Vitamin D, along with calcium, helps to prevent osteoporosis and bone fracture.
Scientists first discovered Vitamin D when studying the effects of Cod Liver Oil. They were already aware of Vitamin A being present in the oil and noticed it prevented rickets in dogs. However, when they used modified CLO in which all the Vitamin A had been destroyed, they noticed it still prevented the disease, and so they realised another substance was responsible. They named it Vitamin D simply as it was the fourth essential dietary substance they had discovered. It wasn’t until later that they found the body could make it on its own.
Few foods contain much Vitamin D, the pick of the bunch being fish and mushrooms. Fortunately, a lot of foods are fortified with it such as milk. It is currently recommended that infants are supplemented with Vitamin D drops, particularly ones being breastfed. This is a result of the reappearance of rickets in children. It probably makes sense. Taking society as a whole, we are spending less and less time outdoors in the presence of sunlight. Elderly people may need Vitamin D supplements as well to aid bone density. Elderly women in particular are at risk of the development of osteoporosis. This can lead to bone fractures if left untreated.
Toxic levels of Vitamin D are rare but can occur. It can raise levels of calcium to dangerous levels which can affect heart function and damage kidneys and blood vessels. Excessive sun exposure cannot cause toxic levels of vitamin D synthesis, as the body will only produce a healthy amount. Overdosage results from an over-ingestion of the vitamin.
Life is full of confusing messages and conflicting information.. One branch of medicine tells us to avoid the sun and wear high factor sunscreen. Another branch tells us to get out in the sunshine more to top up our levels of vitamin D. Like most things in life, it’s a balancing act. All things in moderation.
Cormac Harte M.P.S.I., Mahers Pharmacy, Clonmel, Tel: 052-6121205.