Vitamin D and Winter Health

The RDA (Recommended Dietary Allowance) for adults is 600 IUs (International Units) and the safe upper limit is 4,000 IU of vitamin D supplementation a day for adults.³  Spending 10 to 15 minutes outside on a sunny day with your arms and legs exposed can provide nearly all the vitamin D most people need.  However, obtaining the recommended dose of sunlight exposure may be challenging when wearing long-sleeved uniforms or when most of the daylight time is spent indoors. Vitamin D can be harder to obtain in the wintertime, when it's cold and cloudy and most people spend the majority of their time indoors.     

Increased risk factors⁴    

• Darker skin pigmentation
• Vegans
• Getting less than 15 min of sunshine 2x a week
• Living in northern climates (Canada, northern half of the United States, etc.)
• Wearing long robes and head coverings
• Older adults (> 65)
• Pregnancy and breastfeeding
• Breastfeeding infants
• Obesity (due to tendency for body fat to bind with vitamin D, preventing it to enter the blood).
• Certain digestive problems (e.g., Celiac disease and Crohn's disease)

Vitamin D Deficiency and Bone Health

People can develop vitamin D deficiency over time when their dietary intake is low of vitamin D rich foods or have limited sunlight exposure. Also individuals with kidney disease or conditions preventing adequate absorption of vitamin D from their digestive tract can impact vitamin D status. Diets low in vitamin D are more common in people who have a milk allergy or lactose intolerance and those who consume an ovo-vegetarian (not eating meat, fish, or dairy but will eat eggs) or vegan diet.⁵

Vitamin D deficiency can lead to weak and brittle bones.⁶ Bones are constantly being remodeled. However, as people age—and particularly in women during menopause—bone breakdown rates overtake rates of bone building. Over time, bone density can decline, and osteoporosis can eventually develop.⁷

Osteoporosis is a "silent" disease because you typically do not have symptoms, and you may not even know you have the disease until you break a bone. Osteoporosis is a major cause of fractures in postmenopausal women and in older men.⁸ Osteoporosis is, in part, a long-term effect of calcium and/or vitamin D insufficiency. Osteoporosis is most often associated with inadequate calcium intakes, but insufficient vitamin D intakes contribute to osteoporosis by reducing calcium absorption.⁹

1. Obtain safe sun exposure with exercise outside. Expose your arms and legs to the sun for 10-15 minutes between the hours of 10 a.m. and 3 p.m. For any sun exposure longer than this, apply sunscreen to minimize the risk of skin cancer.

2. Consume vitamin D-rich foods. Very few foods naturally have vitamin D. Fortified foods provide most of the vitamin D in American diets. Fatty fish such as salmon, tuna, and mackerel are among the best sources. Beef liver, cheese, and egg yolks provide small amounts. Most of the U.S. milk supply is fortified with 400 IU of vitamin D per quart, and so are many of the plant-based alternatives such as soy milk, almond milk, and oat milk.  However foods made from milk, like cheese and ice cream, are usually not fortified. Vitamin D is added to many breakfast cereals and to some brands of orange juice, yogurt, margarine, and soy beverages; check the labels.¹⁰ Strive to get at least 600 IUs of Vitamin D every day.  For a complete list of foods, visit http://ods.od.nih.gov/pubs/usdandb/VitaminD-Content.pdf. 

3. Eat enough calcium. Vitamin D and calcium work together to make your bones strong. Make sure you get enough calcium by including a selection of dairy products, leafy vegetables, fish, tofu, Brazil nuts and almonds in your diet. 

Enjoy the winter months with walks in the sunshine along with eating vitamin D and calcium rich foods and beverages for good bone health for the future.