Q: My doctor gave me a prescription for Vitamin D that I’ve taken once a week for the past few months. Now my doctor’s office called and said that I didn’t need another refill, but to continue taking it as a supplement. How much should I take?
Vitamin D plays an important role in maintaining the strength of your muscles and bones. We absorb Vitamin D from the foods we eat and our skin can make it when we are outside on a sunny day, but the form of Vitamin D in our food, in supplements, and in our skin is not yet active. Before it can help us, our kidneys must change that form of Vitamin D into an active one.
As we age our skin makes less Vitamin D from the sun and our kidneys become less efficient in changing it to its active form. Over 50% of elderly Americans are thought to have Vitamin D deficiency, which has been linked to muscle weakness, falling, and an increased risk of breast, prostate, pancreatic, colon and ovarian cancers. Replenishing body stores of Vitamin D with supplementation has been shown to improve muscle strength and balance and decrease falls in elderly Americans by at least 20%.
New evidence published online in November 2014 in the journal Neurology links low levels of Vitamin D to the risk of developing dementia and Alzheimer disease. The Pro.V.A study followed 1927 generally healthy community dwelling elders, comparing blood levels of Vitamin D with their level of mental functioning. Those having a very low level of Vitamin D at the start of the study had a 122% higher risk of experiencing a decline in mental function over the 4.4 years of the study than those with adequate levels. Participants with low levels had a 55% increased risk of cognitive decline compared to the ones with adequate Vitamin D blood levels.
Unfortunately, it’s hard to get enough Vitamin D from just diet alone. The best source is fatty fish such as salmon, canned tuna and sardines, which have about 300 units of Vitamin D per 3.5 ounce serving. The next best source is fortified milk, with up to 100 units of Vitamin D. Milk was fortified in the United States beginning in the 1930s to combat rickets, a deficiency of Vitamin D in children that caused soft bones and deformed legs. One of the most memorable and concentrated sources of Vitamin D is cod liver oil, with 1300 units per tablespoon. (I’ll pass, thanks.)
Vitamin D is called the “Sunshine Vitamin” because our bodies generate it when our skin is exposed to UVB rays in direct sunlight. You are most likely to be deficient in Vitamin D if you are elderly, have dark skin, or spend very little time in the sun without wearing a sunscreen. Other causes of Vitamin D deficiency are linked to poor absorption of fat-soluble vitamins, such as having gastric bypass surgery, inflammatory bowel disease, or taking medicines like prednisone or the weight loss agent Alli®. Alli® is designed to block fat absorption in the gut, decreasing not just dietary fat absorption but also fat-soluble vitamins like Vitamins D and E.
Vitamin D comes in both prescription and non-prescription strengths. Three forms of Vitamin D are available: D2, called ergocalciferol, D3, called cholecalciferol, and calcitriol, which is the active form in our body. All 3 are available without a prescription from 400 up to 4000 units per capsule. The best one to use for maintaining Vitamin D levels is D3, which is cholecalciferol.
If you are considered Vitamin D deficient prescription strength Vitamin D is given: one 50,000 units capsule once a week is usually prescribed for 6-8 weeks, followed by a maintenance dose of 1000 to 2000 units daily. After you have finished the 50,000 once weekly regimen of Vitamin D, if your blood test has come back up to normal you should be able to maintain it with 2,000 units a day from either sun, diet or supplements.
Most women over 50 years old should take a calcium supplement with at least 800 units Vitamin D daily to help their body absorb and use the calcium to strengthen their bones. If you already take a calcium supplement haven’t at least 800 units of Vitamin D, then 1000 units of additional Vitamin D as Vitamin D3 daily should be adequate. Choose Vitamin D3 (cholecalciferol) for best results.
