During the winter, the hours of sunlight decrease. That means fewer opportunities to receive vitamin D, because most people meet some of their vitamin D needs through exposure to sunlight that is scarce in the winter months. Vitamin D synthesis through exposure to the skin is certainly affected by season, but it is also affected by time of day, length of day, cloud cover, smog, skin melanin content, and sunscreen. During the winter months, it is important that we receive adequate amounts of vitamin D because this vitamin is a fat soluble one that is naturally present in very few foods. In addition to exposure to the sun, vitamin D can also be obtained through supplements.

WHY WE NEED VITAMIN D
-promotes calcium absorption in the stomach
-maintains adequate serum calcium and phosphate concentrations needed for normal mineralization of bone. Vitamin D helps our bodies to maintain a good level of calcium and phosphates, and these minerals strengthen and fortify our bones
-prevents symptoms that occur because of a low calcium level, such as brittle and thin bones, rickets (the softening of bones in children), and osteoporosis
-promotes cell growth
-works with the neuromuscular and immune function
-reduces inflammation

HOW MUCH DO WE NEED?
The recommended dietary intake for adults is 600 International units (IU) daily, or 15 micrograms (mcg).

VITAMIN D LINKED TO LONGEVITY
According to Weill Cornell Medical College Women’s Nutrition Connection, researchers observed vitamin D deficiency in one third of 2,638 study participants and found that it was associated with a near 50% increase in their mortality rate. This study was documented in the Journal of Clinical Endocrinology and Metabolism. The participants, ages 70-79 years, were contacted every six months to ascertain their medical condition. Vitamin D lower than 30 ng/ml (nano-grams per milliliter) were associated with significantly increased in deaths.

DIETARY SOURCES OF VITAMIN D
The flesh of fatty fish such as salmon, tuna, and mackerel, as well as fish liver oils, are the best dietary sources for Vitamin D. Small amounts are found in beef liver, cheese, and egg yolks. Fortified foods provide most of the dietary intake of vitamin D in America. Almost all of the U.S. milk supply is voluntarily fortified with 100 international units (IU) of vitamin D per cup. Some ready-to-eat cereals, as well as some brands of orange juice, yogurt, margarine, and other food products are fortified with vitamin D. The U.S. also requires that infant formula be fortified with vitamin D.

It has been suggested by some research that approximately 5-30 minutes of sun exposure between 10am and 3pm at least twice a week to the face, arms, legs, or back without sunscreen is enough to lead to sufficient vitamin D absorption.