The study in a secondary analysis of data from an earlier study that looked at how consumption of freeze dried strawberry powder might affect blood pressure in this group of older women. Both studies were conducted by a group of researchers associated with institutions in Colorado, Florida, Georgia, Texas and Israel. The research was published in the journal Food & Function.
Three-arm study using strawberries
The most recently study was a secondary analysis of a 2017 paper that also appeared in Food & Function. That study was divided into three arms, using 25 grams or 50 grams of the strawberry powder or a placebo. That study looked for how the intervention might improve signs of hypertension or arterial stiffness in a group of postmenopausal women. That study did not find significant effects.
However, the researchers wondered if the intervention might have shown positive effects in terms of osteoporosis, which is a risk for women after menopause. High blood pressure raises this risk. So a secondary analysis of the data was performed looking at measures relevant to this outcome. The authors said they believed this was the first analysis of its type to look at strawberries and bone health for this kind of group.
The study group was recruited in the Tallahassee, FL area (home to Florida State University, one of the institutions associated with the study). Sixty women were recruited and randomly assigned to one of the three groups. Inclusion criteria were having gone through menopause and being diagnoses with pre- and stage-1 hypertension.
In the eight week trial the women consumed daily doses of 25 grams of FDSP (freeze dried strawberry powder), 50 g of FDSP or a placebo, all of which were formulated for the same volume. Those strawberry powder dosages correlated to 1.5 or 3 cups of fresh strawberries daily.
Looking at measures of bone health
For the secondary analysis the researchers looked at measurements such as the level of osteocalcin, adiponectin and IGF-1. Osteocalcin is a protein associated with bone formation while adiponectin is a hormone positively correlated with bone mineral density. IGF-1 (insulin-like growth factor 1) is deemed to be a critical mediator of bone growth.
The researchers found that there was a trend toward higher osteocalcin levels in the 50 gram group, but those differences were not statistically significant.
Similarly, the adiponectin levels increased in both strawberry groups but declined in the placebo group. Once again, these effects did not clear the statistical significance bar.
But the IGF-1 did show a statistically significant increase in the 25 gram strawberry group.
Short duration, group with healthy bones to start with clouded results
Overall bone mineral density did not change significantly for any of the groups, which could be partly due to the fact that while the women had high blood pressure, they all had normal BMD to start with.
The researchers admitted the results were less than bombastic, but noted that bone mineral density is notoriously hard to change, and typically needs months to years to show significant improvement. Thus, shorter term studies fall back onto validated biochemical measures to infer a longer-term benefit. And the original study was targeting blood pressure, which typically will respond over a shorter time scale.
“Overall, our findings suggest that supplementation with 25 g FDSP daily for 8 weeks increases serum levels of IGF-1,” the researchers noted.
“It remains unknown as to whether a longer intervention and perhaps the use of different forms of strawberries would produce different results. Thus, further studies are warranted to address the role of strawberries in bone health of pre- and postmenopausal women and men with and without hypertension and osteoporosis,” they concluded.
Source: Food & Function
2021 Dec 13;12(24):12526-12534. doi: 10.1039/d1fo01555a
Effects of strawberries on bone biomarkers in pre- and stage 1-hypertensive postmenopausal women: a secondary analysis
Authors: Feresin RG, et al.