In the news: Salad Oils Aid Nutrient Absorption; Low Vitamin D Early & Later in Life

Oil in Salad Dressing Helps Absorb Nutrients

Only 9% of Americans eat the 2-3 cups of vegetables recommended daily, and many people consume their vegetables in the form of lettuce and vegetable salads for lunch or dinners, according to consumer surveys.

While the calorie-conscious often avoid using salad dressing, a new study (1) has found that the added oils from dressings enhance the absorption of essential nutrients from salads - namely vitamins E, K, alpha and beta carotene, lutein and lycopene.
 
In the study, each participant consumed five test salads with equivalent vegetable amounts (spinach, romaine lettuce, carrots and cherry tomatoes), but each salad had added dressing with different amounts of soybean oil (0, 2, 4, 8 or 32 g).

The researchers found that nutrient absorption was far lower without any added oil, while the maximum absorption for most nutrients occurred at the 32 g level- a little less than 2 tablespoons of oil.

Soybean oil was tested in this study because it’s the predominant oil used in making bottled salad dressings. However, a previous study showed that oils like canola and olive oil are efficient at promoting the absorption of vegetable’s nutrients as well. The bottom line is that you don’t need to drench a salad with dressing- using a tablespoon or so of olive oil with some vinegar to dress a salad can improve the body’s absorption of important fat-soluble nutrients.

Poor vitamin D Status May Affect Young & Old

Two recently published observational studies suggest that vitamin D deficiency may have consequences in the elderly at risk of heart failure, and in children at risk of type-1 diabetes.

Heart failure, one of the most common reasons people age 65 and older are hospitalized, means that the heart isn’t pumping efficiently enough to meet the body’s need for blood and oxygen. Brazilian university researchers recently report an association between vitamin D deficiency and a higher risk of heart failure in a study of elderly cardiac patients (2). More than half of the 137 elderly patients studied were at risk of heart failure, and that risk was strongly associated with vitamin D deficiency.

About 65% of the patients were deficient based on having blood vitamin D levels less than 30 ng/ml- a higher value than the 20 ng/ml that is more widely used to define deficiency.
 
Vitamin D deficiency was associated with a 12-fold higher risk of heart failure. This was considerably higher than the risks associated with being obese or having cardiac arrhythmia, each of which was linked to about a 4-fold increase heart failure risk.

This is a small study, and one that does not prove cause and effect. However the association has been noted in a few other studies, and the researchers indicate the need for clinical trials with vitamin D supplementation in older patients with heart failure.

In the other vitamin D-related study (3), children with a higher genetic risk for developing type-1 diabetes were checked regularly from infancy to early childhood, and followed in later years. The participants were recruited from the US and across Europe.

Vitamin D levels were determined and researchers looked for antibodies that are detected when insulin-producing islet cells of the pancreas are attacked by the body’s immune system. Called “islet auto-immunity,” the antibodies are considered a precursor to type-1 diabetes.

Comparing vitamin D levels in the early years for those that developed islet autoimmunity with those that did not, showed significantly lower blood levels in those who developed the type-1 precursor. Once again, intervention studies are needed to determine whether vitamin D is a factor in preventing type-1 diabetes. 

References

1. White WS, et al. Modeling the dose effects of soybean oil in salad dressing on carotenoid and fat-soluble vitamin bioavailability in salad vegetables. Am J Clin Nutr 106:1041-51, 2017.
2. Porto CM, et al. Association between vitamin D deficiency and heart failure risk in the elderly. ESC Heart Failure. Epub ahead of print, Aug 2017.
3. Norris JM, et al. Plasma 25-hydroxyvitamin D concen-tration and risk of islet autoimmunity. Diabetes. Epub ahead of print, Oct 2017.