Experts finally agree on one thing in the bottle vs. breastfeeding debate: Regardless of how their mothers choose to feed them, babies need more vitamin D.

The milk of most breastfeeding mothers contains very little vitamin D, and additives in formulas are largely insufficient, says Dr. Robert Heaney, a clinical endocrinologist specializing in nutrition and a professor at Creighton University in Nebraska.

Although vitamin D is important throughout life, it is essential within the first year in reducing risk of current infections and later development of autoimmune diseases such as multiple sclerosis and type 1 diabetes.

Dr. Heaney cites a study published a year ago in the Journal of Clinical Endocrinology & Metabolism that indicates vitamin D plays a crucial role in metabolism and hormonal functioning.

While the amount of vitamin D necessary for adults is debatable, according to Dr. Heaney, the requirements for infants are more obvious. The American Academy of Pediatrics (AAP) and the Institute of Medicine (IOM) recommend 400 IUs delivered daily in drops.

While this number is widely agreed upon as being necessary for infants, Dr. Heaney says that in the case of breastfeeding mothers, milk becomes sufficient in vitamin D when the mother maintains a daily intake between 5,000 and 6,000 IUs.

Mid-day summer sun can help the body produce 10,000 IUs in just one 15-minute, total-body exposure. For those who believe natural is best, this eliminates the need for vitamin D drops, according to Heaney.

Given that the benefits of breastfeeding have long been considered numerous and more beneficial than bottle feeding, surprise is a normal reaction to research that suggests human milk to be insufficient in anything.

A study of indigenous populations of East Africa, published in the European Journal of Nutrition, says that mothers living an ancestral lifestyle not far from the equator produce sufficient levels vitamin D in their milk due to high sun exposure.

Citing this study, Dr. Heaney states that while reverting to ancestral lifestyles and relocating not far from the equator is unnecessary, nursing mothers should receive supplementary doses of vitamin D, enough to match the levels of the East African subjects.

To answer the question of how northern societies survived in the era before vitamin supplements were available, Dr. Heaney says that fish high in vitamin D was their main staple, allowing for sufficient intake.

History highlights the outbreak of rickets a century ago in Europe, North America and East Asia as a sure sign of widespread vitamin D deficiency.

According to Heaney's research, it was eradicated by cod-liver oil and the addition of vitamin D supplements to bottled milk in the 1930s.

Vitamin D is also found in oily fish like salmon and sardines as well as in eggs, milk and shiitake mushrooms.