Vitamin D acts as a hormone in the body and was found to play an important role in the maintenance of calcium levels and bone health almost a century ago. Researchers have recently discovered that vitamin D is also necessary for proper function of the immune system, cardiovascular system, muscles, and brain.
Severe Vitamin D deficiency in childhood can lead to rickets that is characterized by bowed legs, bone and teeth deformities, muscle weakness, and short stature. Rickets has become fairly uncommon in the U.S. due to fortification of milk with Vitamin D beginning in the 1930s, but mild to moderate Vitamin D deficiency continues to be an important problem. Vitamin D deficiency in adults is associated with osteoporosis (brittle bones), increased risk of falls, and possibly fractures.
Recently, low Vitamin D has been associated with increased risk for a number of conditions including muscle weakness, cancers, autoimmune disorders, diabetes, dementia/Alzheimer’s Disease, and cardiovascular disease. Elderly individuals with low Vitamin D levels are at increased risk of falls and have higher death rates. Research into whether Vitamin D supplementation reduces these risks is ongoing.
Eighty to ninety percent of the Vitamin D in our bodies comes from sun exposure. Ultraviolet light from the sun (specifically UVB rays) is used by the skin to make Vitamin D. A fair-skinned person who spends 10 minutes in the midday summer sun – in shorts and a tank top with no sunscreen – will receive enough radiation to produce 10,000 international units (IU) of vitamin D. Dark-skinned individuals and the elderly produce less Vitamin D.
According to the Vitamin D Council, the amount of Vitamin D you get from exposure to the sun depends on:
- The amount of skin you expose – the more skin you expose the more Vitamin D your body will produce.
- The color of your skin – pale skins make Vitamin D more quickly than darker skins.
- The time of day – your skin produces more Vitamin D if you expose it during the middle of the day.
- Where you live – the closer to the equator you live, the easier it is for you to produce Vitamin D from sunlight all year round.
People most prone to a Vitamin D deficiency include those who live in northern regions with little sunlight exposure, people with darker skin, people on low-fat diets, and those taking steroids and weight loss medications. Vitamin D is found naturally in only a few foods such as fish-liver oils, fatty fishes (tuna, mackerel, salmon), egg yolks, and beef liver. In the United States, Vitamin D commonly is added to milk, orange juice, and other foods.
A recent report by the National Health and Nutrition Examination Survey found that approximately 40% of Americans are deficient in Vitamin D, with the highest rates seen in blacks (82%) and Hispanics (69%). There has been an increase in Vitamin D deficiency over the past several decades due to a shift toward indoor work and activities and increased use of sunscreens. One study found that sunscreen with an SPF of 15, when used properly, can reduce Vitamin D formation by as much as 99%. Also, glass blocks UVB rays; so sun exposure through a window does not result in Vitamin D production.
The daily requirement for Vitamin D is at least 600 international units (IU) for adults aged 18-70 and at least 800 IU daily for individuals over 70. There is controversy regarding the recommended daily requirement for Vitamin D, and some groups advocate for as much as 2000 to 5000 IU per day.
You should speak to your doctor before beginning Vitamin D supplements because very high doses of Vitamin D can have negative effects on your health. If you are obese, pregnant, dark-skinned, age 65 or older, or have limited sun exposure, you should talk to your doctor about obtaining a Vitamin D level.
By: Dr. Shanna Ndong
