It’s January in Maine. What should we talk about? Something sexy, exciting and fascinating you say? Well OK! We’ll talk about vitamin D deficiency.
This is a good topic for January, since this is the time of year when many people become deficient in this important vitamin. Our diet often does not provide sufficient amounts of vitamin D and our internal production of the vitamin is essentially zero during winter months (except for those cowards who go to Florida for the winter). Vitamin D production in the body requires skin to be sun-exposed. Just 20 minutes of sun exposure results in significant vitamin D production in most people. But cutaneous (skin) production of vitamin D from sunlight declines with age. People with darkly pigmented skin also produce less vitamin D. Tanning by artificial UVB exposure through tanning beds and sunlamps (but not bright light boxes for winter depression which filter UV light) increases vitamin D production but brings the risks of damaging skin and increasing cancer rates. Recent focus on limiting skin exposure to UV radiation and use of sun screen products has likely contributed to vitamin D deficiency while simultaneously decreasing risk of skin cancer and skin damage. This is a smart trade off, since vitamin D deficiency is easy to fix.
Aside from older and dark-skinned people, those with chronic kidney and liver disease are likely to be low in vitamin D as well. Vitamin D is stored in fat tissue and obesity may contribute to lower levels of the functioning vitamin in the blood. People with poor absorption of nutrients and fats are also likely to be deficient in the vitamin.
Vitamin D is essential for absorbing calcium from food and for maintaining skeletal health. It also plays important (although not fully understood) roles in the function of muscles, nervous system (including brain), immune system and the cardiovascular system. The effects of low vitamin D levels depend on the severity and duration of the deficiency.
Vitamin D is converted to 25-hydroxyvitamin D in the liver and we determine vitamin D deficiency by measuring the amounts of 25-hydroxyvitamin D circulating through the body. This involves a simple blood test. Most experts think that 25-hydroxyvitamin D levels in the range of 30-50 ng/ml are best, but the Institute of Medicine and US Endocrine Society consider concentrations of 20-40 ng/ml to be acceptable. More than 75% of people over 70 in this country have 25-hydroxyvitamin D levels less than 30 ng/ml and more than 25% have levels under 20 ng/ml. There is also a large seasonal variation in blood levels of 25-hydroxyvitamin D, especially at northern latitudes. Levels drop an average of 10 ng/ml between late summer and early spring for people living in northern regions such as Maine. That is, a person with “borderline low” levels in December will almost surely be deficient by March. The US Endocrine Society does not recommend routine screening for vitamin D deficiency. They do however, recommend measuring 25-hydroxyvitamin D levels in people at risk for vitamin D deficiency, such as people with known chronic kidney or liver disease, malabsorption syndromes, inflammatory bowel disease, pregnant and lactating women, dark skinned people, obese people (BMI > 30) and older adults with a history of osteoporosis, falls or fractures.
Vitamin D deficiency causes a rise in parathyroid hormone activity in most people. Parathyroid hormone (PTH) draws calcium from bones and prolonged elevation of PTH over time can cause decalcification of bones (osteomalacia). Severe vitamin D deficiency (25-hydroxyvitamin D levels < 10 ng/ml) leads to more rapid skeletal weakening, bone pain and fractures. There is also fairly strong evidence that adequate vitamin D levels also help maintain muscle strength, reduce fall risk, improve dental health and reduce risk of colorectal cancer, type II diabetes and immune disorders. In fact, hip and shoulder muscle weakness, which are very common in older adults, may be due to vitamin D deficiency. Several studies have shown improvements in muscle strength from vitamin D supplementation. There is evidence that increasing levels of 25-hydoxyvitamin D to greater than 24 ng/ml decreases both falls and fracture risk in older adults. Low vitamin D levels have also been associated with depression and dementia, although the cause and effect relationships are unclear and there is still little evidence that vitamin D supplements would help either depression or dementia.
People who do not get much sun exposure must get vitamin D from their diet or from vitamin supplements. Foods that contain high levels of vitamin D are seafood (wild salmon has 2-3 times as much as farm-raised), egg yolks and mushrooms. Most milk bought in stores is fortified with vitamin D. One cup of milk gives about 100 IU of vitamin D. Dairy products, orange juice and cereals often have supplemental vitamin D to help absorb the calcium found naturally in those foods.
The current recommendations for daily intake of vitamin D is 600 IU per day for adults under age 70 and 800 IU for adults over age 70. These are minimal recommendations and the American Geriatric Society recommends higher amounts; total daily intake from diet and supplements of 2000-4000 IU to ensure 25-hydroxyvitamin D levels >30 ng.ml in >75% of older adults. To achieve this, many people in Maine should take vitamin D supplements during the winter months.
The American Geriatric Society recommends routine supplementation of vitamin D of 1000 IU a day in all adults over age 65 in order to prevent falls and fractures but routine measurement of 25-hydroxyvitamin D is not necessary. If there is concern about adequate absorption, measurement of 25-hydroxyvitamin D is recommended either before or several weeks after supplementation.
Supplements containing vitamin D3 1000 IU daily will increase blood levels 10 ng/ml and should be adequate for most people with mild deficiency in the 25-30 ng/ml range on initial testing. The recommendation of 1000 IU a day of supplemental vitamin D during winter months should compensate for the seasonal reduction in vitamin D. People with other risk factors for vitamin D deficiency may need higher levels of supplementation and people who spend little time outdoors may need vitamin supplements year-round. The American Geriatric Society also recommends calcium supplementation in the range of 500 to 1200 mg/day for those taking vitamin D.
Weekly, bi-weekly and monthly dosing with vitamin D3 (cholecalciferol) at higher amounts may be necessary for certain people, up to 50,000 IU monthly or biweekly orally or by injections. Vegans may choose to take vitamin D2 from non-animal sources. Taking vitamin D with high fat meals may enhance absorption, whereas taking it with oatmeal and high fiber cereals may hinder absorption. Higher levels than 40-50 ng/ml are probably not helpful and may even cause to over-absorption of calcium from food, which can lead to several kinds of health problems.
What I’ve tried to do in this month’s column is to make you aware of the high risk you face of vitamin D deficiency living in Maine through the winter and how older adults are especially at risk. I’ve also tried to give you a basic understanding of the science of vitamin D and the rationale for published recommendations for taking vitamin D supplements. The recommendation of taking vitamin D3 supplements of 1000 IU a day is widely considered to be safe for routine use, but I strongly suggest that you discuss these recommendations with your health care provider as you may have some health conditions or take certain medications that would alter your vitamin D requirements or the amount of supplementation you need. They may also interpret the published guidelines differently than I have. They may suggest an alternate strategy, such as naked skiing.